sadly I cannot help today off-hand, but the good news is, that I have to sort out a conference payment quite soon. I know that the payment feature had some issues in version 14/15 which have been fixed by Jonny.
If somebody else knows the setup off-hand, hints are welcome.
Give me a day or two and I will look into it and share my findings. I also have already some imagination about the setup and tested a (long) while ago.
So we will get there definitely.
Best regards, will be hearing from each other soon.