OpenProject Integration - link on existing Project or work packages

Hi, I have a problem linking files in nextcloud to existing projects or work packages in OpenProject. Nextcloud doesn’t see them. Reverse sync works. Does anyone know where the problem is?

Log from nextcloud:

OpenProject API error : Client error: POST https://openproject.zidlochovice.cz/api/v3/work_packages resulted in a 422 Unprocessable Content response: {“_type”:“Error”,“errorIdentifier”:“urn:openproject-org:api:v3:errors:PropertyConstraintViolation”,“message”:"Projekt ne (truncated…)