Assuming this is about the CampaignEvents software.

Is the user trying to associate the edit on hewiki, or on meta? Revision IDs are local, so they need to be added in the same wiki where the edit was made.

That would explain the error. The event is exclusively on Meta-Wiki, but it tracked multiple-wikis, so this behaviour is unexpected. Would it be possible to provide the whole url or select the wikiproject + revision, so that it can include it? Otherwise, the event-tracking...is rather limited

The contribution CANNOT be added even from the local Wikipedia. I do not see an “add edit” interface anywhere in the link you shared with me. I enclose screenshots of HeWiki and MetaWiki for comparison. It’s same on both desktop and mobile. I appreciate that this is a new feature and UX improvements still being made to find these URLs more easily

Ah, I see the issue is that as an event creator, I cannot add contributions on any projects, but other participants confirmed it works for them, so I will close this bug, as it is related to T321823, which I still didn't understand until today. I am now registered, and can confirm it works.

In T436978#12292451, @Shushugah wrote:

The contribution CANNOT be added even from the local Wikipedia. I do not see an “add edit” interface anywhere in the link you shared with me.

In T436978#12292507, @Shushugah wrote:

Ah, I see the issue is that as an event creator, I cannot add contributions on any projects, but other participants confirmed it works for them

Yup. To clarify, organizers can only add other people's edits on the main wiki of the event, because of permission checks. It is true that they cannot add edits made on other wikis, and that will be addressed in T437091. However, participants can add their own edits (and only those) on any wiki.