It's worth considering that Vetter/Mopla (or employees of it) have been known to share the private key (which is used to validate D-Tickets sold by them) to third parties who then issue fraudulent D-Tickets to customers while not providing the collected revenue to the German government.
This has meant that, in the past, people who thought they bought valid tickets have found themselves issued with fines all of a sudden when this private key becomes marked as cancelled.
Illegal Telegram stores offer fake Deutschlandtickets: Almost 1200 tickets from various transport associations investigated indicate "triangular fraud".
www.heise.de
My understanding based on recent conversation with the group that initially uncovered the first round of fraud in Feb is that this has now happened
again a few days ago, and another process of invalidating existing tickets is likely going to take place soon.
Given Vetter/Mopla do not appear to adhere to the rules for selling D-Tickets, I'd recommend not using them. It seems as though the current D-Ticket fraud has totalled approx €300mn revenue in the last 10 months alone. Similarly, I'd definitely have second thoughts buying any D-Tickets from anything except the local transport authority or DB.