Sony Vegas Pro 15 Won't Open

Registration date
Monday March 9, 2015
Last seen
June 18, 2021
Hey everyone. I hope you had a great Thanksgiving.

I would really appreciate any help you may provide. I bought Sony Vegas Pro 15 for my son from Amazon in November 2019. He's been using it with no problems until last week. Now, it will not open because it needs a registration code.
But, he's evidently misplaced the box with everything in it. I have my Amazon invoice as proof of purchase.

It would really make my day (and his) if someone could help me.