Wash. Rev. Code § 48.18.370
Whenever the proceeds of, or payments under a life or disability insurance policy, heretofore or hereafter issued, become payable and the insurer makes payment thereof in accordance with the terms of the policy, or in accordance with any written assignment thereof pursuant to RCW 48.18.360, the person then designated in the policy or by such assignment as being entitled thereto, shall be entitled to receive such proceeds or payments and to give full acquittance therefor, and such payment shall fully discharge the insurer from all claims under the policy unless, before payment is made, the insurer has received at its home office, written notice by or on behalf of some other person that such other person claims to be entitled to such payment or some interest in the policy.
RCW 48.18.370