Prescription Coordination of Benefits

I am covered by two health insurance plans, as of Jan. 1st my primary plan is no longer the HMO, here is info on both:

-Primary Plan: PPO -PBM: Express Scripts -Requires STEP therapy for certain medication, cost subject to change based on meeting deductible.

-Secondary Plan: HMO -PBM: Express Scripts/Prime Therapeutics -No STEP requirement, flat co pay of $25 for prescriptions.

I take a controlled substance that needs to be filled monthly, it has not been an issue to fill with my HMO. Now that the PPO is the primary, I understand that the pharmacy will try to run it through that insurance first. It should be denied because the STEP therapy has not been done and my doctor has not requested a PA. (I am not willing to stop taking the med that I have been on for the last 5 years to complete the STEP therapy, or wait for a PA.) When this happens does the pharmacy then run it against my secondary insurance? So I should be able to get my medication without issues? I cannot find ANY information on how coordination of benefits works with pharmacies. Can anyone shed some light on this?

TLDR; how does coordination of benefits work for medications?