The All-in-One WP Migration plugin communicates with your Dropbox account and stores your backups using the Dropbox API. You may receive one of these errors if there is an error communicating with your storage and the files stored there.
Dropbox assigns a per-user quota to each user to distribute resources fairly. You may experience problems if you have a large number of other applications or systems linked to your Dropbox account.

What can you do about it?

If the all-in-One WP Migration plugin is unable to connect to your Dropbox account, please sign out and sign back in in the Dropbox Settings page of the plugin on your WordPress Console.
Make sure no other apps are using your Dropbox at the same time as the All-in-One WP Migration extension. Consider stopping or uninstalling any third-party Dropbox applications or services. Consider an alternative to Dropbox if you share a large number of documents with others or the general public.

Please see the list of error codes below for more information:

Invalid Credentials
The All-in-One WP Migration Plugin is unable to connect to your Dropbox account. Please sign out of your account and sign back in to the Dropbox Settings of the WordPress plugin in your WordPress Console.

The user does not have sufficient permissions for the file
The All-in-One WP Migration Plugin is unable to access any files or folders on your Dropbox account. Please ensure that the file or folder you are attempting to access with the plugin is accessible via your Dropbox account.
If this does not work, or if the file is already on your drive, please sign out of your Dropbox account and sign back in to the Dropbox Settings page of the plugin in your WordPress Console.

Cannot be used within the domain
The All-in-One WP Migration Plugin does not have access to your Dropbox account. If you’re attempting to backup or migrate your site while logged in on a corporate domain, make sure you can access your Dropbox storage or contact the domain administrator.

File not found
The All-in-One WP Migration Plugin is unable to access any files or folders on your Dropbox account. Please double-check that the file exists and that you can access it via your drive.

Backend Error
While processing the request, your Dropbox encountered an unexpected error. Please try once more. Please sign out of your account and sign back in on your WordPress Console’s Dropbox Settings page.

Bad Request
The All-in-One WP Migration Plugin is unable to connect to your Dropbox account. Please sign out of your account and sign back in to the Dropbox Settings of the WordPress plugin in your WordPress Console.
User Rate Limit Exceeded
On your drive, there have been an excessive number of API calls. After stopping drive sync and any other applications that connect to your drive and waiting 5 minutes, try again.

Rate Limit Exceeded
On your drive, there have been an excessive number of API calls. After stopping drive sync and any other applications that connect to your drive and waiting 5 minutes, try again.

Sharing Rate Limit Exceeded
You have exceeded your Dropbox account’s sharing rate limit. This could be related to emails or documents that you have publicly shared from your drive. When performing backups/migrations, avoid sending large volumes of emails. Remove permissions from publicly accessible files on your drive.

The user has not granted access to the file
The All-in-One WP Migration Plugin is unable to access any files or folders on your Dropbox account. Please ensure that the file or folder you are attempting to access with the plugin is accessible via your cloud account. If this does not work, or if the file is already on your drive, please sign out of your account and sign back in to the Dropbox Settings page of the WordPress plugin in your WordPress Console.

Too Many Requests
Your Dropbox account has received an excessive number of requests. This could be related to documents that you are publicly sharing from your drive or other applications that use Dropbox.

Here is a complete list of HTTP error codes including their meaning in Dropbox API:

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Code: 400 ‘Bad Request’
Bad input character.

Code: 401 ‘Unauthorized’
Bad or expired token. This can happen if the access token is expired or if the access token has been revoked by Dropbox or the user. To fix this, you should re-authenticate the user.

Code: 402 ‘Payment Required’
You must pay for the product in order to proceed.

Code: 403 ‘Forbidden’
The user or team account doesn’t have access to the feature.

Code: 404 ‘Not Found’
The requested resource doesn’t exist.

Code: 405 ‘Method Not Allowed’
The resource does not allow the HTTP method in the request.

Code: 406 ‘Not Acceptable’
This service doesn’t support the format requested in the Accept header. The requested resource is capable of generating only content not acceptable according to the Accept headers sent in the request.

Code: 407 ‘Proxy Authentication Required’
Proxy authentication required. The client must first authenticate themselves with the proxy.

Code: 408 ‘Request Timeout’
Request timed out. The server timed out waiting for the request. The client did not produce a request within the time that the server was prepared to wait. Repeat the request without modifications at any later time.

Code: 409 ‘Conflict’
The current state conflicts with what the request expects. The conflict does not allow the request to process.

Code: 410 ‘Gone’
The requested resource is no longer available at the server.

Code: 411 ‘Length Required’
The request requires a Content-Length based header.

Code: 412 ‘Precondition Failed’
The server does not meet one of the preconditions that the requester put on the request.

Code 413 ‘Request Entity Too Large’
The request size exceeds the maximum limit.

Code 414 ‘Request-URI Too Long’
Request-URI too long. The URI provided was too long for the server to process.

Code: 415 ‘Unsupported Media Type’
The service does not support the content type of the request format.

Code: 416 ‘Requested Range Not Satisfiable’
The specified byte range is invalid or unavailable.

Code: 417 ‘Expectation Failed’
Expectation failed. The server cannot meet the requirements of the Expect request-header field.

Code: 429 ‘Too Many Requests’
The client application is making too many requests for the given user and it is being rated limited.

Code: 5xx
An error occurred on the Dropbox servers. Check status.dropbox.com for announcements about Dropbox service issues.

Code: 500 ‘Internal Server Error’
There was an internal error while processing the request.

Code: 501 ‘Not Implemented’
The requested feature is not implemented.

Code: 502 ‘Bad Gateway’
Bad gateway. The server was acting as a gateway or a proxy and received an invalid response from the upstream server.

Code: 503 ‘Service Unavailable’
The service is temporarily unavailable. You may repeat the request after a delay. There may be a Retry-After header.

Code: 504 ‘504 Gateway Timeout’
The server was acting as a gateway or proxy and did not receive a timely response from the upstream server.

Code: 505 ‘HTTP Version Not Supported’
The server does not support the HTTP protocol version used in the request.

Here is a complete list of cURL error codes:

CURLE_OK (0)
All fine. Proceed as usual.

CURLE_UNSUPPORTED_PROTOCOL (1)
The URL you passed to libcurl used a protocol that this libcurl does not support. The support might be a compile-time option that you didn’t use, it can be a misspelled protocol string or just a protocol libcurl has no code for.

CURLE_FAILED_INIT (2)
Very early initialization code failed. This is likely to be an internal error or problem, or a resource problem where something fundamental couldn’t get done at init time.

CURLE_URL_MALFORMAT (3)
The URL was not properly formatted.

CURLE_NOT_BUILT_IN (4)
A requested feature, protocol or option was not found built-in in this libcurl due to a build-time decision. This means that a feature or option was not enabled or explicitly disabled when libcurl was built and in order to get it to function you have to get a rebuilt libcurl.

CURLE_COULDNT_RESOLVE_PROXY (5)
Couldn’t resolve proxy. Could not resolve the given proxy host.

CURLE_COULDNT_RESOLVE_HOST (6)
Couldn’t resolve host. Could not resolve the given remote host.

CURLE_COULDNT_CONNECT (7)
Failed to connect() to host or proxy.

CURLE_FTP_WEIRD_SERVER_REPLY (8)
The server sent data libcurl couldn’t parse. This error code is used for more than just FTP and is aliased as CURLE_WEIRD_SERVER_REPLY since 7.51.0.

CURLE_REMOTE_ACCESS_DENIED (9)
We were denied access to the resource given in the URL. For FTP, this occurs while trying to change to the remote directory.

CURLE_FTP_ACCEPT_FAILED (10)
While waiting for the server to connect back when an active FTP session is used, an error code was sent over the control connection or similar.

CURLE_FTP_WEIRD_PASS_REPLY (11)
After having sent the FTP password to the server, libcurl expects a proper reply. This error code indicates that an unexpected code was returned.

CURLE_FTP_ACCEPT_TIMEOUT (12)
During an active FTP session, while waiting for the server to connect, the CURLOPT_ACCEPTTIMEOUT_MS (or the internal default) timeout expired.

CURLE_FTP_WEIRD_PASV_REPLY (13)
libcurl failed to get a sensible result back from the server as a response to either a PASV or a EPSV command. The server is flawed.

CURLE_FTP_WEIRD_227_FORMAT (14)
FTP servers return a 227-line as a response to a PASV command. If libcurl fails to parse that line, this return code passes back.

CURLE_FTP_CANT_GET_HOST (15)
An internal failure to lookup the host used for the new connection.

CURLE_HTTP2 (16)
A problem was detected in the HTTP2 framing layer. This is somewhat generic and can be one out of several problems, see the error buffer for details.

CURLE_FTP_COULDNT_SET_TYPE (17)
A problem was detected in the HTTP2 framing layer. This is somewhat generic and can be one out of several problems, see the error buffer for details.

CURLE_PARTIAL_FILE (18)
Received an error when trying to set the transfer mode to binary or ASCII.

CURLE_FTP_COULDNT_RETR_FILE (19)
This was either a weird reply to a ‘RETR’ command or a zero byte transfer complete.

CURLE_QUOTE_ERROR (21)
When sending custom “QUOTE” commands to the remote server, one of the commands returned an error code that was 400 or higher (for FTP) or otherwise indicated unsuccessful completion of the command.

CURLE_HTTP_RETURNED_ERROR (22)
This is returned if CURLOPT_FAILONERROR is set TRUE and the HTTP server returns an error code that is >= 400.

CURLE_WRITE_ERROR (23)
An error occurred when writing received data to a local file, or an error was returned to libcurl from a write callback.

CURLE_UPLOAD_FAILED (25)
Failed to start the upload. For FTP, the server typically denied the STOR command. The error buffer usually contains the server’s explanation for this.

CURLE_READ_ERROR (26)
There was a problem reading a local file or an error returned by the read callback.

CURLE_OUT_OF_MEMORY (27)
A memory allocation request failed. This is serious badness and things are severely screwed up if this ever occurs.

CURLE_OPERATION_TIMEDOUT (28)
Operation timeout. The specified time-out period was reached according to the conditions.

CURLE_FTP_PORT_FAILED (30)
The FTP PORT command returned an error. This mostly happens when you haven’t specified a good enough address for libcurl to use. See CURLOPT_FTPPORT.

CURLE_FTP_COULDNT_USE_REST (31)
he FTP REST command returned an error. This should never happen if the server is sane.

CURLE_RANGE_ERROR (33)
The server does not support or accept range requests.

CURLE_HTTP_POST_ERROR (34)
This is an odd error that mainly occurs due to internal confusion.

CURLE_SSL_CONNECT_ERROR (35)
A problem occurred somewhere in the SSL/TLS handshake. You really want the error buffer and read the message there as it pinpoints the problem slightly more. Could be certificates (file formats, paths, permissions), passwords, and others.

CURLE_BAD_DOWNLOAD_RESUME (36)
The download could not be resumed because the specified offset was out of the file boundary.

CURLE_FILE_COULDNT_READ_FILE (37)
A file is given with FILE:// couldn’t be opened. Most likely because the file path doesn’t identify an existing file. Did you check file permissions?

CURLE_LDAP_CANNOT_BIND (38)
LDAP cannot bind. LDAP bind operation failed.

CURLE_LDAP_SEARCH_FAILED (39)
LDAP search failed.

CURLE_FUNCTION_NOT_FOUND (41)
Function not found. Could not find a required zlib function.

CURLE_ABORTED_BY_CALLBACK (42)
Aborted by callback. A callback returned “abort” to libcurl..

CURLE_BAD_FUNCTION_ARGUMENT (43)
Internal error. A function was called with a bad parameter.

CURLE_INTERFACE_FAILED (45)
Interface error. Could not use a specific outgoing interface. Set which interface to use for outgoing connections’ source IP address with CURLOPT_INTERFACE.

CURLE_TOO_MANY_REDIRECTS (47)
Too many redirects. When following redirects, libcurl hit the maximum amount. Set your limit with CURLOPT_MAXREDIRS.

CURLE_UNKNOWN_OPTION (48)
An option passed to libcurl is not recognized/known. Refer to the appropriate documentation. This is most likely a problem in the program that uses libcurl. The error buffer might contain more specific information about which exact option it concerns.

CURLE_TELNET_OPTION_SYNTAX (49)
A telnet option string was Illegally formatted.

CURLE_GOT_NOTHING (52)
Nothing was returned from the server, and under the circumstances, getting nothing is considered an error.

CURLE_SSL_ENGINE_NOTFOUND (53)
The specified crypto engine wasn’t found.

CURLE_SSL_ENGINE_SETFAILED (54)
Failed to set the selected SSL crypto engine as default!

CURLE_SEND_ERROR (55)
Failed sending network data.

CURLE_RECV_ERROR (56)
Failure with receiving network data.

CURLE_SSL_CERTPROBLEM (58)
Problem with the local client certificate.

CURLE_SSL_CIPHER (59)
Couldn’t use the specified cipher.

CURLE_PEER_FAILED_VERIFICATION (60)
The remote server’s SSL certificate or SSH md5 fingerprint was deemed not OK. This error code has been unified with CURLE_SSL_CACERT since 7.62.0. Its previous value was 51.

CURLE_BAD_CONTENT_ENCODING (61)
Unrecognized transfer encoding.

CURLE_LDAP_INVALID_URL (62)
Invalid LDAP URL.

CURLE_FILESIZE_EXCEEDED (63)
Maximum file size exceeded.

CURLE_USE_SSL_FAILED (64)
Requested FTP SSL level failed.

CURLE_SEND_FAIL_REWIND (65)
When doing a send operation curl had to rewind the data to retransmit, but the rewinding operation failed.

CURLE_SSL_ENGINE_INITFAILED (66)
Initiating the SSL Engine failed.

CURLE_LOGIN_DENIED (67)
The remote server denied curl to login (Added in 7.13.1)

CURLE_TFTP_NOTFOUND (68)
File not found on TFTP server.

CURLE_TFTP_PERM (69)
Permission problem on TFTP server.

CURLE_REMOTE_DISK_FULL (70)
Out of disk space on the server.

CURLE_TFTP_ILLEGAL (71)
Illegal TFTP operation.

CURLE_TFTP_UNKNOWNID (72)
Unknown TFTP transfer ID.

CURLE_REMOTE_FILE_EXISTS (73)
File already exists and will not be overwritten.

CURLE_TFTP_NOSUCHUSER (74)
This error should never be returned by a properly functioning TFTP server.

CURLE_CONV_FAILED (75)
Character conversion failed.

CURLE_CONV_REQD (76)
The caller must register conversion callbacks.

CURLE_SSL_CACERT_BADFILE (77)
Problem with reading the SSL CA cert (path? access rights?)

CURLE_REMOTE_FILE_NOT_FOUND (78)
The resource referenced in the URL does not exist.

CURLE_SSH (79)
An unspecified error occurred during the SSH session.

CURLE_SSL_SHUTDOWN_FAILED (80)
Failed to shut down the SSL connection.

CURLE_AGAIN (81)
The socket is not ready for send/recv to wait till it’s ready and try again. This return code is only returned from curl_easy_recv and curl_easy_send (Added in 7.18.2)

CURLE_SSL_CRL_BADFILE (82)
Failed to load CRL file (Added in 7.19.0)

CURLE_SSL_ISSUER_ERROR (83)
Issuer check failed (Added in 7.19.0)

CURLE_FTP_PRET_FAILED (84)
The FTP server does not understand the PRET command at all or does not support the given argument. Be careful when using CURLOPT_CUSTOMREQUEST, a custom LIST command will be sent with PRET CMD before PASV as well. (Added in 7.20.0)

CURLE_RTSP_CSEQ_ERROR (85)
Mismatch of RTSP CSeq numbers.

CURLE_RTSP_SESSION_ERROR (86)
Mismatch of RTSP Session Identifiers.

CURLE_FTP_BAD_FILE_LIST (87)
Unable to parse FTP file list (during FTP wildcard downloading).

CURLE_CHUNK_FAILED (88)
Chunk callback reported an error.

CURLE_NO_CONNECTION_AVAILABLE (89)
(For internal use only, will never be returned by libcurl) No connection available, the session will be queued. (added in 7.30.0)

CURLE_SSL_PINNEDPUBKEYNOTMATCH (90)
Failed to match the pinned key specified with CURLOPT_PINNEDPUBLICKEY.

CURLE_SSL_INVALIDCERTSTATUS (91)
The status returned failure when asked with CURLOPT_SSL_VERIFYSTATUS

CURLE_HTTP2_STREAM (92)
Stream error in the HTTP/2 framing layer.

CURLE_RECURSIVE_API_CALL (93)
An API function was called from inside a callback.

CURLE_AUTH_ERROR (94)
An authentication function returned an error.

CURLE_OBSOLETE*
These error codes will never return. They were used in an old libcurl version and are currently unused.