Hi Graham.
I don't quite understand how would he do that.
Would he need a type of activity (mod plugin) that handles payment in every course or maybe even for every module and then base the condition on that?
Does such a module exist?
Or would he add some invisible random activity and have another payment handling plugin set it as completed? That sounds kind of messy.
I guess I'm not completely understanding your approach, and would like to know more.
Thanks for any info.