Migration fails: Object of type filter is not JSON serializable

Symptoms

• Migration fails with the following error:

  Failed to fetch configuration data from Plesk servers
  Cause: Object of type filter is not JSON serializable
  That is a critical error, migration was stopped.

Cause

Plesk Migrator bug #PMT-5353, which was fixed in Plesk Migrator 2.26.1 on August, 7.

Resolution

1. Log into Plesk

2. Update the Plesk Migrator extension.
3. Re-start migration process.