How to manually lower the commit_fee for channels?

[ShookLyngs]

Say A opens a channel of 20,000 sats to B and pushes 1,000 sats to B. Since the current fee rate on testnet is high, A now has 785 sats in balance, while B has 1,000. The latest commit_fee is 17,555 sats.

The problem is that even though A seems to have sufficient balance for a 1 sat transfer to B (or conversely, B should be able to transfer 1 sat to A), the transfer fails with the following error:

FAILED, reason: FAILURE_REASON_INSUFFICIENT_BALANCE

A then tries to update the lnd.conf to the following, even providing a static JSON via the fee.url parameter:

max-channel-fee-allocation=0.1
max-commit-fee-rate-anchors=1
fee.url=https://raw.githubusercontent.com/ShookLyngs/test-lnd-fee-url/refs/heads/main/static-fees.json
fee.min-update-timeout=1m
fee.max-update-timeout=1m1s

However, the commit_fee remains high at the original value of 17,555. How can A force an update to the commit_fee except waiting for the network fees to drop, for example, setting it to a very low value so that it doesn't block the entire transaction process? By the way, A is using bitcoind as the backend node.

[guggero]

What channel type is the channel in question?

[ShookLyngs]

What channel type is the channel in question?

It's an ANCHORS type channel. In theory with the static fee.url set, providing fee_by_block_target and min_relay_feerate as low as 1012, the fee rate should have been lowered by the random timeout update_fee event. However, in reality, the channel was not updated for a long time (about a day or so). Here's an error related to the channel; I suppose it's about updating the fee:

[WRN] LNWL: ChannelPoint(x:0): Set available amount to 0 because we could not pay for the CommitmentFee of the new ChannelState: ourBalance is negative after applying the fee: ourBalance=17986000, current commitFee(w/o additional htlc)=17555000 mSAT, feeBuffer=20241000 mSAT (type=additionalhtlc) local_chan_initiator

I then deposited more coins into A's L1 address and opened another channel with the lnd.conf mentioned above (static fee.url and more, just to limit the commit_fee). This time, when the new channel was opened, both channels' fee rate was updated, the new channel's fee rate was 250, the old one was 253.

While the old channel was able to facilitate transfers between A and B, the new channel, on the other hand, was unable to make transfers because its fee rate was 250, which was too low to be accepted. This warning appears in the logs:

[WRN] CRTR: ShortChannelID=x: cannot add outgoing htlc: commitment fee per kw 250 sat/kw below fee floor 253 sat/kw