Issues (Error 500) with IDs/Names out of sync between Mautic and DPAG

[ekkeguembel]

Describe the bug
Error 500 with log messages like these show up
500 Internal Server Error - Es existiert bereits ein Print-Mailing mit dem externen Bezeichner "6".
500 Internal Server Error - Ein Datensatz konnte nicht gefunden werden: 0.
Es existiert bereits ein Print-Mailing mit diesem Namen.

Situations where these occur:

• The same DPAG account is (or has been) used by multiple instances
• Things have been deleted on the Mautic side but not on the DPAG side
• The DPAG account has been changed in this Mautic
• a user is giving the same name twice

Expected behavior

• For Print Mailing Templates in Mautic, Mautic should not allow the same name twice
• Before persisting a Print Mailing, Mautic should verify if that name exists, and if so: deny usage and remain in creation form ("name already exists in DPAG, please choose a different one")
• Before persisting a Print Mailing, Mautic should verify if the intended ID , and if so: Increase by one and try again

Ideally, Mautic should be able to fetch all existing print mailings and add all missing ones to the List of Print Mailings (mark them as "imported; needs mapping verification"). But that's not for here; I'll create a different story :)

Mautic Plugin version
4.4

Plugin version
4.1

[ekkeguembel]

same uncaught 500, but different error message: "Es existiert bereits ein Print-Mailing mit diesem Namen." after trying to create a template with a previously used name