Unable to connect to Remote Storage using Plesk Backup extensions: Error: Class 'GuzzleHttp\Promise\<ClassName>' not found

Symptoms

• Unable to connect to Google Drive Backup at Plesk > Tools & Settings > Backup Manager > Remote Storage Settings: Upon logging into the Google account and returning to Plesk, instead of showing Google's account details to finish configuring the backup, only a "Cancel" button is shown:

  

• Unable to connect to Amazon S3 Backup at Plesk > Tools & Settings > Backup Manager > Remote Storage Settings. The following error appears in Plesk:

  PLESK_ERROR: Internal error
  ERROR: Error: Call to undefined method GuzzleHttp\Promise\Coroutine::of() (functions.php:362)[...]

Cause

Plesk Bug #PAUX-3748, which will be fixed in a future update.

Resolution

In the meantime, the following workaround can be applied:

1. Connect to the server via SSH;

2. Copy the PHP class files from platform360 into the required extension directory. For example:

   • To fix Google Drive Backup:

     # cp -a /usr/local/psa/admin/plib/modules/platform360/vendor/guzzlehttp/promises/src/*.php /usr/local/psa/admin/plib/modules/google-drive-backup/vendor/guzzlehttp/promises/src/

   • To fix Amazon S3 Backup:

     # cp -a /usr/local/psa/admin/plib/modules/platform360/vendor/guzzlehttp/promises/src/*.php /usr/local/psa/admin/plib/modules/s3-backup/vendor/guzzlehttp/promises/src/

     On rare occasions, missing file might not be under the platform360 directory. In this case, search for the file in all extensions and copy it manually:

     For ie: for Utils.php

     # find /usr/local/psa -name Utils.php | grep modules

     Then copy the file for the necessary extension, for example SpamExperts:

     # cp -a /usr/local/psa/admin/plib/modules/wp-toolkit/vendor/guzzlehttp/promises/src/Utils.php /usr/local/psa/admin/plib/modules/spamexperts-extension/library/vendor/guzzlehttp/promises/src/

3. Log into Plesk;

4. Go to Tools & Settings > Backup Manager > Remote Storage Settings and configure the desired remote storage extension.