Payjoin client incompatibility with BIP78

[kristapsk]

Current implementation of Payjoin client in BTCPay isn't compatible with BIP78, as it encodes request in hex, not base64. Tested with JoinMarket payjoin receiver and it fails.

Likely this line needs to be changed, but I don't have test environment for that right now (I used testnet.demo.btcpayserver.org) -

btcpayserver/BTCPayServer/Services/PayjoinClient.cs

Line 317 in f88c02c

new StringContent(originalTx.ToHex(), Encoding.UTF8, "text/plain"), cancellationToken);

.

See zkSNACKs/WalletWasabi#4427.

[Kukks]

Thanks, fixed it for the next release