I’m trying to understand how Lightning works by running tests using Bitcoin Core on my local machine in REGTEST mode and also running two LND Lightning nodes (let’s call them default Bob & Alice) on separate localhost ports. I am using bitcoin-cli and lncli Interfaces with the node.
I linked Alice’s LN to Bob’s LN and opened a channel between them with an initial capacity of 10,000,000 sats, funded by Alice’s chain wallet. --pushamt Bob’s LN is allocated 35,000 to generate some inbound liquidity. This all seemed to be going as expected and the financing deal was 2of2 multi-signature Content covering channels has also been added to the blockchain (6 confirmed).
But nonetheless, something was wrong. Even though Alice sent BTC over the channel, Bob cannot send that BTC back to Alice. I even had Bob send Alice an invoice for 5,000 Saturdays, but after she paid them, nothing changed (except that the remote balance increased to 40,000 Saturdays). Still, Bob can’t send her even 1 Saturday using her channel’s channel. inbound liquidity! I don’t understand why.
Session state from Alice’s perspective (local/remote is reversed for Bob, of course):
$ lncli --lnddir=lnd_alice -n regtest openchannel --connect 127.0.0.1:9736 --node_key 030fb4423c15e3e049dbbdc646d0ef3ab7450a891652bbe0c39a14a8f5b44dc15f --sat_per_vbyte 1 --local_amt 10000000 --push_amt 35000 --block --base_fee_msat 1000 --fee_rate_ppm 10 --min_confs 1
"funding_txid": "df79c5246a3f1f8dfd6c983106b743a8220a1f4c819b76aeb41d69ccfc2baf4e"
"channel_point": "df79c5246a3f1f8dfd6c983106b743a8220a1f4c819b76aeb41d69ccfc2baf4e:0"
$ lncli --lnddir=lnd_alice -n regtest listchannels
"channels": (
"active": true,
"remote_pubkey": "030fb4423c15e3e049dbbdc646d0ef3ab7450a891652bbe0c39a14a8f5b44dc15f",
"channel_point": "df79c5246a3f1f8dfd6c983106b743a8220a1f4c819b76aeb41d69ccfc2baf4e:0",
"chan_id": "513471930236928",
"capacity": "10000000",
"local_balance": "9961530",
"remote_balance": "35000",
"commit_fee": "2810",
"commit_weight": "1116",
"fee_per_kw": "2500",
"unsettled_balance": "0",
"total_satoshis_sent": "0",
"total_satoshis_received": "0",
"num_updates": "0",
"pending_htlcs": (),
"csv_delay": 1201,
"private": false,
"initiator": true,
"chan_status_flags": "ChanStatusDefault",
"local_chan_reserve_sat": "100000",
"remote_chan_reserve_sat": "100000",
"static_remote_key": false,
"commitment_type": "ANCHORS",
"lifetime": "80",
"uptime": "80",
"close_address": "",
"push_amount_sat": "35000",
"thaw_height": 0,
"local_constraints":
"csv_delay": 1201,
"chan_reserve_sat": "100000",
"dust_limit_sat": "354",
"max_pending_amt_msat": "9900000000",
"min_htlc_msat": "1",
"max_accepted_htlcs": 483
,
"remote_constraints":
"csv_delay": 1201,
"chan_reserve_sat": "100000",
"dust_limit_sat": "354",
"max_pending_amt_msat": "9900000000",
"min_htlc_msat": "1",
"max_accepted_htlcs": 483
,
"alias_scids": (),
"zero_conf": false,
"zero_conf_confirmed_scid": "0",
"peer_alias": "unable to lookup peer alias: alias for node not found",
"peer_scid_alias": "0",
"memo": ""
)
$ lncli --lnddir=lnd_alice -n regtest channelbalance
"balance": "9961530",
"pending_open_balance": "0",
"local_balance":
"sat": "9961530",
"msat": "9961530000"
,
"remote_balance":
"sat": "35000",
"msat": "35000000"
,
"unsettled_local_balance":
"sat": "0",
"msat": "0"
,
"unsettled_remote_balance":
"sat": "0",
"msat": "0"
,
"pending_open_local_balance":
"sat": "0",
"msat": "0"
,
"pending_open_remote_balance":
"sat": "0",
"msat": "0"
$ lncli --lnddir=lnd_alice -n regtest getchaninfo --chan_point "df79c5246a3f1f8dfd6c983106b743a8220a1f4c819b76aeb41d69ccfc2baf4e:0"
"channel_id": "513471930236928",
"chan_point": "df79c5246a3f1f8dfd6c983106b743a8220a1f4c819b76aeb41d69ccfc2baf4e:0",
"last_update": 1733192887,
"node1_pub": "030fb4423c15e3e049dbbdc646d0ef3ab7450a891652bbe0c39a14a8f5b44dc15f",
"node2_pub": "03f23e9d775b5363a2311742209fc4d50eb47e8c226b78472609356f9d72294729",
"capacity": "10000000",
"node1_policy":
"time_lock_delta": 80,
"min_htlc": "1000",
"fee_base_msat": "1000",
"fee_rate_milli_msat": "1",
"disabled": false,
"max_htlc_msat": "9900000000",
"last_update": 1733192887,
"custom_records": ,
"inbound_fee_base_msat": 0,
"inbound_fee_rate_milli_msat": 0
,
"node2_policy":
"time_lock_delta": 80,
"min_htlc": "1000",
"fee_base_msat": "1000",
"fee_rate_milli_msat": "10",
"disabled": false,
"max_htlc_msat": "9900000000",
"last_update": 1733192887,
"custom_records": ,
"inbound_fee_base_msat": 0,
"inbound_fee_rate_milli_msat": 0
,
"custom_records":
$ lncli --lnddir=data/lnd_alice -n regtest --rpcserver=127.0.0.1:10010 sendpayment --pay_req="lnbcrt1pn5ulwxpp5hleus2vrjx29ercwtxuzgyrpl8ckkexmprlm9eps0nrl4jn30mpsdqqcqzzsxqyz5vqsp55zavqw9rv5xfxnw6vucluqfrspazwfz7hl4hsqhagnhvrkywyuls9p4gqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqpqysgqlm77eh73g68dkxy4pjf4stjc3tg6yxf9z6ua5l0axjn4tznw2lpsjcdnu8gvug9r095wmg8v56jhmhqzvgz4ch6lmhgrues2hvqe6rspdmdxd5" --amt=5000
Payment hash: bff3c8298391945c8f0e59b8241061f9f16b64db08ffb2e4307cc7faca717ec3
Description:
Amount (in satoshis): 5000
Fee limit (in satoshis): 250
Destination: 030fb4423c15e3e049dbbdc646d0ef3ab7450a891652bbe0c39a14a8f5b44dc15f
Confirm payment (yes/no): yes
+------------+--------------+--------------+--------------+-----+----------+-----------------+----------------------+
| HTLC_STATE | ATTEMPT_TIME | RESOLVE_TIME | RECEIVER_AMT | FEE | TIMELOCK | CHAN_OUT | ROUTE |
+------------+--------------+--------------+--------------+-----+----------+-----------------+----------------------+
| SUCCEEDED | 0.016 | 0.152 | 5000 | 0 | 555 | 513471930236928 | 030fb4423c15e3e049db |
+------------+--------------+--------------+--------------+-----+----------+-----------------+----------------------+
Amount + fee: 5000 + 0 sat
Payment hash: bff3c8298391945c8f0e59b8241061f9f16b64db08ffb2e4307cc7faca717ec3
Payment status: SUCCEEDED, preimage: 47f028b0b825f07e8325735c3e84541e7f5e982635136cee32dff590a21465eb
$ lncli --lnddir=data/lnd_alice -n regtest --rpcserver=127.0.0.1:10010 channelbalance
"balance": "9956530",
"pending_open_balance": "0",
"local_balance":
"sat": "9956530",
"msat": "9956530000"
,
"remote_balance":
"sat": "40000",
"msat": "40000000"
,
"unsettled_local_balance":
"sat": "0",
"msat": "0"
,
"unsettled_remote_balance":
"sat": "0",
"msat": "0"
,
"pending_open_local_balance":
"sat": "0",
"msat": "0"
,
"pending_open_remote_balance":
"sat": "0",
"msat": "0"
$ lncli --lnddir=data/lnd_alice -n regtest --rpcserver=127.0.0.1:10010 feereport
"channel_fees": (
"chan_id": "513471930236928",
"channel_point": "df79c5246a3f1f8dfd6c983106b743a8220a1f4c819b76aeb41d69ccfc2baf4e:0",
"base_fee_msat": "1000",
"fee_per_mil": "10",
"fee_rate": 0.00001,
"inbound_base_fee_msat": 0,
"inbound_fee_per_mil": 0
),
"day_fee_sum": "0",
"week_fee_sum": "0",
"month_fee_sum": "0"
Bob wants to pay some of those BTC back to Alice using the same Lightning channel that Alice opened and funded.
$ lncli --lnddir=data/lnd_bob -n regtest --rpcserver=127.0.0.1:10009 sendpayment --pay_req="lnbcrt1pn5u778pp5xe7ey4lxnevntdveqaaxwtjw29j3yqqtrqqgdxqxylckjndsd56qdqqcqzzsxqyz5vqsp574v9pxu5lja7mjn9uv95uu3mep64w7w00gsedjsse94h2t0xq2zq9p4gqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqpqysgqs0z2xmy9a0un69k8xpp7x2nl8z5ryn25n8n8fet78adax327ksvyll4wdk6s2h58yg8gw8mdqre288uc3edagpg8ave4l8rnxz3kz7sqxj2dhu" --amt=2000
Payment hash: 367d9257e69e5935b599077a672e4e516512000b180086980627f1694db06d34
Description:
Amount (in satoshis): 2000
Fee limit (in satoshis): 100
Destination: 03f23e9d775b5363a2311742209fc4d50eb47e8c226b78472609356f9d72294729
Confirm payment (yes/no): yes
+------------+--------------+--------------+--------------+-----+----------+----------+-------+
| HTLC_STATE | ATTEMPT_TIME | RESOLVE_TIME | RECEIVER_AMT | FEE | TIMELOCK | CHAN_OUT | ROUTE |
+------------+--------------+--------------+--------------+-----+----------+----------+-------+
+------------+--------------+--------------+--------------+-----+----------+----------+-------+
Amount + fee: 0 + 0 sat
Payment hash: 367d9257e69e5935b599077a672e4e516512000b180086980627f1694db06d34
Payment status: FAILED, reason: FAILURE_REASON_INSUFFICIENT_BALANCE
(lncli) FAILED
$ lncli --lnddir=lnd_bob -n regtest --rpcserver=127.0.0.1:10010 channelbalance
"balance": "40000",
"pending_open_balance": "0",
"local_balance":
"sat": "40000",
"msat": "40000000"
,
"remote_balance":
"sat": "9956530",
"msat": "9956530000"
,
"unsettled_local_balance":
"sat": "0",
"msat": "0"
,
"unsettled_remote_balance":
"sat": "0",
"msat": "0"
,
"pending_open_local_balance":
"sat": "0",
"msat": "0"
,
"pending_open_remote_balance":
"sat": "0",
"msat": "0"
$ lncli --lnddir=lnd_bob -n regtest --rpcserver=127.0.0.1:10010 listpeers
"peers": (
"pub_key": "03f23e9d775b5363a2311742209fc4d50eb47e8c226b78472609356f9d72294729",
"address": "127.0.0.1:60194",
"bytes_sent": "92017",
"bytes_recv": "82927",
"sat_sent": "0",
"sat_recv": "5000",
"inbound": true,
"ping_time": "974",
"sync_type": "ACTIVE_SYNC",
"features":
"0":
"name": "data-loss-protect",
"is_required": true,
"is_known": true
,
"5":
"name": "upfront-shutdown-script",
"is_required": false,
"is_known": true
,
"7":
"name": "gossip-queries",
"is_required": false,
"is_known": true
,
"8":
"name": "tlv-onion",
"is_required": true,
"is_known": true
,
"12":
"name": "static-remote-key",
"is_required": true,
"is_known": true
,
"14":
"name": "payment-addr",
"is_required": true,
"is_known": true
,
"17":
"name": "multi-path-payments",
"is_required": false,
"is_known": true
,
"23":
"name": "anchors-zero-fee-htlc-tx",
"is_required": false,
"is_known": true
,
"25":
"name": "route-blinding",
"is_required": false,
"is_known": true
,
"27":
"name": "shutdown-any-segwit",
"is_required": false,
"is_known": true
,
"31":
"name": "amp",
"is_required": false,
"is_known": true
,
"45":
"name": "explicit-commitment-type",
"is_required": false,
"is_known": true
,
"2023":
"name": "script-enforced-lease",
"is_required": false,
"is_known": true
,
"errors": (),
"flap_count": 7,
"last_flap_ns": "1733192845755233591",
"last_ping_payload": "00000020d22b2aa43b49ef1fd79d668a09a6562f0e40ffe75eeda662d978cb3d5454290af3b209f13de7fec7f63fc2f4c361db7bb10606af6622289890316905c5da663db6884e67ffff7f2001000000"
)
$ lncli --lnddir=lnd_bob -n regtest --rpcserver=127.0.0.1:10010 queryroutes --dest 03f23e9d775b5363a2311742209fc4d50eb47e8c226b78472609356f9d72294729 --amt 2000
(lncli) rpc error: code = Unknown desc = insufficient local balance
It seems that the only way for Bob to send funds back to Alice would be for Bob to open his own separate channel and send the payments (i.e. outbound liquidity) through it. I don’t understand why inbound liquidity on Alice channel is not working.
We appreciate your comments, suggestions, and additional questions!