I'm no cryptobro whatsoever, but reading earlier discussions, especially with the whole how do you know who sent money and who didn't, wouldn't something among the lines of a receipt from a wallet or something like that work? I get that crypto probably isn't the best solution out there, but it sure seems like a solid one in this situation, especially if no payment provider is willing to cooperate.
Please don't sue me over my lack of understanding in the crypto world, I'm not really in it, but if i have to buy like 20 bucks worth of bitcoin, eutherum, or something like that, I'm willing to do so