Whenever an agreement or supplemental agreement shall be executed between an employer and employe or his dependents as provided by this act, such agreement shall be executed in triplicate. Two copies thereof, signed by all parties in interest, shall be mailed or delivered to the department within thirty days after execution. It shall be the duty of the department to examine the agreement to determine whether it conforms to the provisions of section four hundred and seven,¹ to notify the parties thereto of its validity or invalidity, under the aforesaid section, within thirty days after the copies of the agreement have been mailed or delivered to it, and, if the agreement be approved, to send to the employe or dependents, together with such notification of its approval, a copy of the agreement: Provided, however, That any payment made in accordance with any agreement prior to the receipt of notice of invalidity shall discharge pro tanto the liability, under article three of this act,² of the employer making such payments.