GoodRx isn't really a third party. They contract with real third party payers like Navitus and Optum. And those contracts the real third parties have with the pharmacy are what are contractually enforceable. So that contract you signed with Optum has the requirement that you accept GoodRx claims built in because those are really Optum claims via the GoodRx middleman. Being that each contract with each individual PBM is a mix of lower and higher reimbursements, you typically make money on each contract as a whole. But being armed with numerous third party contracts, GoodRx can cherry pick the best deals from multiple PBMs and offer rates to consumers that frequently make pharmacies lose money. That's why when you do a drug search on their site, you always get random BINs and PCNs depending on the drug you want a discount card for. Back in the day, discount cards weren't that bad. They were for one processor and one processor only. Your profit would still ebb and flow, but overall, money was still there to be made. With GoodRx, you have to match the best price for several processors and are forced to lose money all the time.
So GoodRx makes money on each claim, the PBMs are fine with this because they get a cut, and the pharmacy is there at the end holding the bag. It's actually quite a brilliant scheme. Some rando Silicon Valley dweebs that signed a few predatory contracts are stealing your profits for basically creating a simple search engine and laying in the cut.
If I were an independent pharmacy owner, I'd be on the dark web trying to contract some hacking group from like Latvia with Bitcoin to coordinate an endless DDOS attack on GoodRx and Singlecare. But, alas, I work for CVS so IDGAF.