Billing Question

BCBS has been really protracted in approving my application to join the network (they told me the wrong paperwork to complete somehow and made me restart) and I’ve had multiple prospective clients waiting 2+ months for me to be able to accept their insurance.

Does anyone know/had success with seeing a patient and charging their copay rate at the time of sessions, then billing for the previously held sessions once the contract with BCBS is signed? I assume I’d have to ask for a backdated contract, which I’m hopeful I could maybe get since I have emailed proof that their agent told incorrectly around what to complete.