Is it a prerequisite to submit proof of actual payment of legal fees for compensation to be awarded for them?

That is not a prerequisite. The concept of damage for which compensation is due encompasses both actual damage incurred and damage certain to occur in the future. The establishment of the obligation to pay legal fees upon the fulfillment of a specific condition (such as the issuance of a judicial judgment) is considered a damage certain to occur. The susceptibility of this obligation to waiver or assignment does not affect this, as opening the door to such contingencies could lead to entirely precluding compensation for litigation fees.