On a different site, a small test payment worked, but with Ethereum, and only after changing the "Country" field to something different.
So either I'm being sanctioned (??), or my coins are being rejected for taint (which is diabolical as these coins come from change addresses fed from an Altcoinstalks address).
I know that Altcoinstalk allows advertising mixers and that's the reason many accounts from Bitcointalk have migrated there to continue earning fees from such advertisement. I assume that's also what you are doing. If the coins have in the past been connected to mixers and coinjoins, that might be the reason your payments are being rejected. Unfortunately, too many services have bought into the whole 'taint' problem and some coins are worth more to them than others. You could easily test if that is true by making a payment using an UTXO that doesn't originate from something these gullible service providers would classify as tainted.