If someone is based in the US and signs up for Preferred, the first rental doesn't show on the board. They have to go to the counter and have the counter agent see their credit card (the linked credit card which is used for all their automatic Preferred rental payments).

In fact, you also have to visit the counter again if your linked card number changes. (So even though I've used the same card for about a decade, once or twice I got a new card number from the bank due to fraud issues, and on those cases I had to go back to the counter one more time.)

So there are lots of possiblities I see:

1. You haven't linked a credit card at all.

2. Perhaps only a rental in your home country can be that first one where they verify everything at the counter.

3. Even if prepaids work later on, maybe prepaid rentals can't be used to that first rental where they establish your linked card is valid, because since it's prepaid you don't need to show your linked card?

(I'm assuming here, though you didn't state, that you're only using prepaid rates you found on the Avis site, and thus your Wizard number is still linked in. Obviously, if you are using prepaid rates on a third-party site, it may not even be possible to like you Wizard number in. And you cannot get Preferred service on a rental which does not have your Wizard number linked in. So, for example, forget about buying rentals as part of a vacation "package" sold by an airline, in that case the airline puts its own Wizard number in.)