It would be great to mention in the documentation that the foreign UUID key of a child element is mandatory to have as a HIDDEN field a relation editor widget work properly in a parent feature form. I just spent about 4 hours tinkering with a project to understand why the one-to-many wasn't working properly within the mobile app while seeming to work fine in QGIS. I think many users would intuitively remove the foreign UUID key from the drag and drop designer, but it really has to be there for things to work.
It would be great to mention in the documentation that the foreign UUID key of a child element is mandatory to have as a HIDDEN field a relation editor widget work properly in a parent feature form. I just spent about 4 hours tinkering with a project to understand why the one-to-many wasn't working properly within the mobile app while seeming to work fine in QGIS. I think many users would intuitively remove the foreign UUID key from the drag and drop designer, but it really has to be there for things to work.