[bug]: Asset Channel Payment Fails with "FAILURE_REASON_NO_ROUTE"

[shuishihang]

I created four litd nodes named A, B, C, and D, and all of them hold the same asset. I established asset channels between A and B, between B and C, and between C and D using the same asset. Now, I generated an asset invoice on node D and attempted to pay it from node A, but the payment failed with the error: "Payment failed: FAILURE_REASON_NO_ROUTE"

[guggero]

The issue is that all asset channels are a sub type of Taproot channels. And because those look differently on chain than previous channel types, we need an update to the specification for those to be announced to the network.
The consequence of that is that currently all asset channels are private. So A and B in your scenario don't know about the channel between C and D. And A doesn't know about the channel between B and C.
If you have an invoice, that invoice will contain a so-called route hint for the last edge. So A would learn about the channel CD from the invoice, but it would still not know about channel BC.

Since the idea is that asset channels are only used "at the edge of the network", that would mean that the "core" of the network would be made up of normal, non-asset public channels. So in your scenario, the channel between B and C should be a normal, BTC-only public channel (of the anchors type, not taproot so it can be announced to the network) so all other nodes can learn about it and use it for routing.

Then B and C would be so-called "edge nodes" that convert from/to assets for their end-user nodes A and D.

[shuishihang]

Thank you, I understand now, but why was A able to successfully pay when I created an asset invoice using C?

[guggero]

Because A knows about the channel AB and the invoice contains a "route hint" for the channel BC, which completes the route. But if you try to pay D, then the invoice route hint only contains CD and A is missing the information for the channel BC (it won't remember those channels that were previously in invoices).

Closing the issue as "won't fix" as asset channels at the edge will likely remain private even in the future. But feel free to comment further if you have more questions.

[shuishihang]

Thank you very much, I think I have a general understanding now.

[shuishihang]

I encountered an issue with the asset channel. Every time Alice makes a payment to Bob, it always carries 354 satoshis. Is it possible to configure this amount to be reduced further?

[guggero]

No, that's the minimum amount to be above the dust limit. See #888.
There will be a workaround in the future, but that will take some time: lightningnetwork/lnd#9430

So currently that's by design until a more custom solution is implemented.

[shuishihang]

Why does this error occur?
rpc error: code = Unknown desc = error funding channel: unable to fund PSBT: unableto fund psbt: rpc error: code = Unknown desc = error selecting coins: not enoughwitness outputs to create funding transaction,need 0.00258625 BTC only have
0.00142629 BTC available

[shuishihang]

At first, the error was:
rpc error: code = Unknown desc = error funding channel: unable to fund PSBT: unable to fund psbt: rpc error: code = Unknown desc = error selecting coins: not enough witness outputs to create funding transaction, need 0.00100000 BTC only have 0.00079000 BTC available.

Now, the error is:
rpc error: code = Unknown desc = error funding channel: unable to fund PSBT: unable to fund psbt: rpc error: code = Unknown desc = error selecting coins: not enough witness outputs to create funding transaction, need 0.00258625 BTC only have 0.00142629 BTC available.

[shuishihang]

Now there is another change:
rpc error: code = Unknown desc = error funding channel: unable to fund PSBT: unable to fund psbt: rpc error: code = Unknown desc = error selecting coins: not enough witness outputs to create funding transaction, need 0.00311500 BTC only have 0.00142629 BTC available.