Backups to a remote storage cannot be completed in Plesk: An internal error occurred. Please retry your upload

Symptoms

• A backup to the remote storage (like Backblaze or any s3 storage) fails in Plesk:

PLESK_ERROR: Warning: Subscription "example.com"
Unable to create the remote backup: Transport error: Extension transport: ext://s3-backup/server/: An internal error occurred. Please retry your upload.

• The backup may work on retry or next attempt

Cause

Temporary connectivity issues on a remote storage side.

Resolution

To increase the number of resume attempts for failed uploads from Plesk side, perform the following:

1. Log into Plesk.

2. Install the Panel.ini Editor from the Extensions menu in Plesk.

3. Go to Extensions > My Extensions > Panel.ini Editor. 

4. Switch to the Editor tab.

5. Scroll down to the button and add the following lines there:

   CONFIG_TEXT: [ext-s3-backup]
   MaxResumeAttempts = 50
   MaxResumeFailures = 50

Plesk will perform more attempts to resume upload in case connection to s3 storage fails for some reason.