42 CFR § 422.520(b)(1-2)

(1) Contracts between MA organizations and providers and suppliers. Contracts or other written agreements between MA organization and providers must contain a prompt payment provision, the terms of which are developed and agreed to by both the MA organization and the relevant provider.

(2) The MA organization is obligated to pay contracted providers under the terms of the contract between the MA organization and the provider. (Emphasis added.)