Retail licensees may use payment services to facilitate retail sales transactions under the following conditions:

(1) The payment service provider must:

(a) If applicable, be licensed and in good standing with the Washington state department of financial institutions; and

(b) Not have any interest, as a true party of interest or financier, in a marijuana licensee.

(2) The payment service provider may charge a convenience fee to customers provided that the customer has the option of canceling the transaction when informed of the convenience fee.

(3) The retail purchase price must be calculated in U.S. dollars.

(4) The marijuana excise tax required under RCW 69.50.535 must be collected from the customer based on the U.S. dollar purchase price.