A few solutions could solve this issue. The first, encouraging more RP, is that pledges can run payment from their gang leader to the medics, who would then be encouraged to keep track through notes of who they treat and what is owed. Secondly, medics can do the same noting practice, and reach out to a certain gang NPC at the end of the week to sort out payment.
If anyone has any thoughts on other solutions, or support for something like this, please share! Just trying to gauge whether this is a personal issue of something the community notices as well. Could provoke some interesting RP and improve NPC interactions/ambience.