Is it legal for a doctor not to charge copay or lower the surgery and accept only what insurance pays?

It is generally illegal for doctors to charge patients less than the copayment or coinsurance amount required by their insurance. This practice is known as "balance billing" or "surprise billing." Doctors must bill the patient's insurance company for the allowed amount and can only collect the remaining balance from the patient. However, there are a few exceptions to this rule. For example, doctors can charge patients less if they have a "provider-patient agreement" that waives the patient's responsibility to pay any remaining balance. Additionally, doctors can balance bill patients if they are out-of-network providers and the patient has not agreed to pay the balance.