Prior to the Acts of Union in the 16th century, Welsh and English Law differed. Welsh Law was codified in the 10th century, during the reign of Hywel Dda, and included laws relating to the rights and treatment of women One of these required that the first time a husband slept with his wife, he would make a payment to her called the ‘morning gift’ (cowyll) in recognition of the loss of her virginity. This is probably what is meant here.
The ‘maiden-fee’ (amobr), on the other hand, was the payment a father made to his feudal lord on the same occasion.
Another reference to the maiden fee is to be found in ‘How Culhwch Won Olwen'.