Don't think I need an attorney here - this is not an complicated one. So far I made all contracts i needed myself and had no problems. Just some research to cover all points and that's it. I'm not after an advice, but a sample. I take all the risks.
Glad to help. Sorry you did not hear me. Money is involved, Facebook is involved (third party) with you being First Party thus significant for possible litigation. There are few, if any, boilerplate contracts available on the web to accomplish your goal. I'm not a lawyer, but have been in business long enough (40 years) to know that I would need one to get this critter done. That said YMMV