This part is not applicable when, upon January 1, 2021, a local governing body is a party to a valid contract that includes terms related to the collection and remittance of the taxes set out in §67-4-1502(a), with a short-term rental unit marketplace. This section applies only while the contract, or any successor agreement, remains valid and effective. If the contract terminates and no successor agreement is executed, then the taxes must be collected and remitted in accordance with this part.