Unable to migrate a database in Tools & Settings > Migration & Transfer Manager > source server or via Site import extension, when a database username has more than 16 characters:
Unable to create database user 'usernamewith16characters' in subscription 'example.com': Command execution failed on the local server with non-zero exit code.
command: /usr/local/psa/bin/database --create-dbuser usernamewith16characters -passwd '' -domain example.com -any-database -type mysql -server localhost:3306 -ignore-nonexistent-options
exit code: 1
stderr: Unable to add database user: Database user name is invalid.
The issue is considered as a Plesk bug with id #PPM-1889 which is already fixed in Plesk Obsidian.
Upgrade to Plesk Obsidian to use up to 32 characters in MySQL 5.7 or up to 80 characters in MariaDB 10.0 and higher versions:
As a workaround: