d11n

I have it almost working, fiddling with the details right now.

Done now, ready for review :)

@petzsch Thanks for the pointer, [f8eae35](https://github.com/btcpayserver/btcpayserver-docker/pull/516/commits/f8eae35674a02bf89c38cf0bf2a2fdf4e873b5f3) contains the fix.

## How to test Prerequisite: You need a non-pruned node, the fragment opt-add-mempool is incompatible with pruning. Go to your BTCPay Server directory and run the following commands: ```bash #...

@ndeet Yes, the requirement for ElectrumX leads to the incompatibility there. Updated the How To Test comment, thanks for the pointer!

@petzsch I think this needs to be fixed on the application level. We are rewriting some of the content with nginx `sub_filter` already, but I'd refrain from rewriting parts of...

That sounds kinda related to this one in the Deployment FAQ: [With the docker deployment, how to use a different volume for the data?](https://docs.btcpayserver.org/FAQ/Deployment/#with-the-docker-deployment-how-to-use-a-different-volume-for-the-data)

Alright, maybe then @Bangalisch and @petzsch can collaborate on improving the [With the docker deployment, how to use a different volume for the data?](https://docs.btcpayserver.org/FAQ/Deployment/#with-the-docker-deployment-how-to-use-a-different-volume-for-the-data) FAQ entry.

@gruve-p @NicolasDorier Yes, I can confirm that setting the "Always include non-witness UTXO" fixes the problem. Can we circumvent this issue by detecting if it is a hardware wallet that...

The PSBT one is about to sign gets created before we even know which wallet will be used for signing. I think we need to tackle this differently -- maybe...