Okay, I've now investigated this.
It seems like most of the payments were taking quite a while to process so now that they've all come through, I can get some of the money. The bad side is that after processing fees it comes to about half of what people donated. (This is the problem with very small payments on this sort of platform - Patreon's got a somewhat better deal with the processors, but it's still better to avoid stuff less than $3 there.)
As I don't want Paypal or Mastercard to be basically taking half of what people try to give to our project, I'll leave the donations off for now, although in future I do plan to sell the commercial versions on here.