The following warning message appears in Plesk when migrating a subscription or during the restoration of a backup from another Plesk server:
The PHP handler 5.5 FPM application (id=fpm) is not available on the destination server.
Instead, Plesk will use the following PHP handler: 5.5.38 FPM application served by Apache (id=plesk-php55-fpm)
The PHP version installed on the source server is not installed on the target server, and Plesk suggests using another installed PHP version.
This warning message can be safely ignored.
In case it's required to keep using the same PHP version, install it on the target server following the steps described here: How to install/remove additional PHP versions provided by Plesk