Hi @Phil_Seeman
Thank you so much for the thorough explanation. I unfortunately stumbled a bit too late over this post … reading that first could’ve spared the both of us some time 
It’s been very helpful to have you walk through the process, and I suppose we’ll land on the approach where we just delete any attachments that the On submit callback produces.
Of course, we’ll try @Bastien_Siebman’s approach as well – if that works, that’s definitely preferable and indeed what we wanted to achieve in the first place.
Thank you both!