500 Internal Server Error when confirming list subscription twice

[NicoHood]

Version:

• listmonk: 2.1.0

Description of the bug and steps to reproduce:
A client of us triggered a very "nice" edge case bug: When you click the opt-in button twice of a mail, listmonks shows a 500 Server error. This message comes from the webserver, not listmonk itself and it a lot confusing for non-technical people.

It should show rather a message "You've already opted in" or so.

[NicoHood]

What would the UI now show?

[knadh]

The message remains the same. There are no subscriptions to confirm. The incorrect status code (500) is fixed.

[NicoHood]

Wouldn't it make sense to add a message, that the subscribtion was already confirmed? If that differenciation is not possible, maybe something like There are no subscriptions to confirm. Maybe they have already been confirmed? would be better?