A Lightning channel in a non-custodial Lightning implementation, such as in the Relai app, represents a private "tunnel" between the user and the Lightning Service Provider (LSP). The channel enables fast transactions with low fees. Instead of anchoring each transaction in the blockchain, the channel is operated outside the blockchain, i.e. "off-chain". This makes the Lightning Network ideal for smaller and frequent payments.
Fees
When you open a Lightning channel, two fees must be taken into account:
Bitcoin network fee:
This fee is incurred when the user sends BTC to the LSP, regardless of whether a new Lightning channel needs to be opened or an existing Lightning channel is used for a SWAP-in. The Bitcoin network fee depends on the current network activity and pays the miners for adding the transaction to the Bitcoin blockchain.
Channel opening fee:
The channel opening fee is a service fee charged by the LSP to set up and maintain the Lightning channel. This fee currently corresponds to 0.4% of the amount transferred. In addition, a dynamic minimum fee is set, which adjusts according to the current Bitcoin network fees. The 0.4% of the transferred amount will only be charged as a fee if it exceeds the dynamic minimum fee.
The channel opening fee will only be charged if a new channel is necessary or the existing inbound liquidity is not sufficient for the planned transfer of OnChain BTC to Lightning BTC.
Inbound liquidity is the liquidity that can be received in a Lightning channel. You can find information about your inbound liquidity in your Relai app under -> Profile -> Settings -> Lightning information.
To summarise:
The Bitcoin network fee is incurred when the user sends BTC to the LSP, be it for the opening of a new Lightning channel or for the exchange of OnChain BTC into Lightning BTC, even if there is sufficient inbound liquidity in an existing large channel.
The channel opening fee is a service fee charged by the LSP for setting up and maintaining the channel.
Additional information on receiving Lightning transactions:
If you want to receive BTC via the Lightning network, but there is not enough inbound liquidity in the existing Lightning channel, the LSP opens a new channel and adds additional liquidity to this channel, among other things. This additional liquidity currently amounts to 50k SATS.
For example, if you want to receive 60,000 SATS, but there is not enough inbound liquidity in the current channel, the LSP opens a new channel with 110,000 SATS.