Update project_invoice.py

odex25_project/project_base/models/project_invoice.py

@@ -231,7 +231,11 @@ class ProjectInvoice(models.Model):
 
     def action_set_to_draft(self):
         self.ensure_one()
-        self.state = 'draft'
+        if self.invoice_id.state=='draft':
+            self.invoice_id=False or [(5, 0, 0)]
+            self.state = 'draft'
+        else:
+            raise UserError(_("Kindly The invoice is not in draft state, so it cannot be unlinked."))
 
     def action_get_invoice(self):
         self.ensure_one()