Where is "is not a member of the budget's project" in the solution 

I'm translating what I read, even though I find it strange.

Strange that's "budget's project" and not "project's budget".

Ok. Solved in Crowdin.

=> https://fr.crowdin.com/project/openproject

09:59

Vous avez été mentionné dans le projet OpenProject

Chaîne : "is not a member of the budget's project"

Jens Ulferts (julferts):

@Moosh-be , @rbrevetti , a Project can have multiple budgets. E.g. one for 2026 and one for 2027. Therefore, it is correct that the string refers to the "members of the budget's project". Because this is an error message the current user is presented with when choosing a user to be planned for in the budget (e.g. 30 hours done by user XYZ in the budget for 2026) when that user is not even member in the project the budget is for.