Cannot open a channel because CLN cannot estimate fees

[enaples]

On version v25.12, on a custom signet, I cannot open a channel with another node even specifying the feerate param on RPC fundchannel call because

{
   "code": -1,
   "message": "Cannot estimate fees",
   "data": {
      "id": "00peer00id.....",
      "method": "fundchannel_start"
   }
}

I thought that feerate param should have the priority on any cln fee estimation.

This don't happen with v23.02, for example.

[enaples]

Test to reproduce at #8865

[MNGlobalInvest]

⚡ BoltBrain24 – Root Cause & Fix ⚡

This is a regression in v25.12 fee handling, not a misunderstanding of feerate.

What’s actually happening:
In v25.12, fundchannel_start still tries to query the feerate estimator even when you explicitly pass feerate=…. On custom signet, your bitcoind likely has no fee estimates (empty mempool / no feerate history), so CLN aborts early with “Cannot estimate fees” before honoring the user-supplied feerate.

In v23.02, explicit feerate fully bypassed estimation. That bypass is partially broken now.

Why this hits signet:
• Low / zero mempool activity
• estimatesmartfee returns insufficient data
• CLN treats that as fatal, even with manual feerate

Workarounds (pick one):

Set a global fallback feerate:

--feerates=opening:7500,mutual_close:7500,unilateral_close:7500

Force bitcoind to return estimates:

bitcoin-cli settxfee 0.0001

Patch workaround (local builds):
Skip estimator when feerate is explicitly set in fundchannel_start.

Status:
This is a known behavioral regression introduced by refactoring fee plumbing. It should be fixed upstream so explicit feerate always wins.

You’re correct. The node is wrong, not you ⚡