Below is the Telephone Consumer Protection Act (47 C.F.R. 64.1200(f)(9)) which defines prior express written consent which is required for TCPA compliance.

(9) The term prior express written consent means an agreement, in writing, bearing the signature of the person called that clearly authorizes the seller to deliver or cause to be delivered to the person called advertisements or telemarketing messages using an automatic telephone dialing system or an artificial or prerecorded voice, and the telephone number to which the signatory authorizes such advertisements or telemarketing messages to be delivered.

(i) The written agreement shall include a clear and conspicuous disclosure informing the person signing that:

(A) By executing the agreement, such person authorizes the seller to deliver or cause to be delivered to the signatory telemarketing calls using an automatic telephone dialing system or an artificial or prerecorded voice; and

(B) The person is not required to sign the agreement (directly or indirectly), or agree to enter into such an agreement as a condition of purchasing any property, goods, or services.

(ii) The term “signature” shall include an electronic or digital form of signature, to the extent that such form of signature is recognized as a valid signature under applicable federal law or state contract law.

Here is a checklist TCPA checklist for you to review.