DCA and Create (form) on UX



I have trouble with the creation of a new item in my module using Create form on the UX.

I have the error " Failed to create item ".
The line item that is in my module is ruled by a DCA, allowing it to be editable only when the "Modify?" boolean is checked by the end user.

Do you have any idea on how can I manage to get rid of this error, but still be able to edit line item on "modify?" click ?

Thank you very much