Once an on-chain wallet is created, you can then start opening an off-chain payment channels with peers of your choice and use them to send payments across the Lightning network.
Technically speaking, a payment channel is a multisig lockbox on a blockchain which is mutually controlled by you and a peer of your choice. A certain amount of on-chain coins is locked into the channel and you can use those coins to send and receive off-chain Lightning payments.
You can close a payment channel and get the rest of your locked coins back to your on-chain wallet at any time, either by agreeing with a peer on a mutual closing transaction (which occurs quickly) or via forced channel closing if your peer does not respond or becomes uncooperative.
It is safe to have many copies of the same on-chain wallet which is restored from the same mnemonic phrase running on different phones but only one of those phones should have open channels. Otherwise there is a risk of all your channels being force-closed by remote peers due to communication issues. This is how LN works, sad but true.
Both you and your peer always have the option to forcefully close an opened payment channel, without the other’s permission. This will refund your off-chain balance back into your on-chain wallet after a certain delay which is usually set to 144 blocks (about 24 hours).
An outgoing Lightning payment may get stuck due to a buggy or malicious node along the payment route. If this happens you will have to wait until it expires, which may take quite a number of blocks. Once it expires the payment will fail and the in-flight funds will be refunded back to your wallet.
In order to receive Lightning payments, some conditions must be met:
Nothing can be received immediately after creating a new payment channel, as ‘room’ for incoming funds has to be made by spending some funds first. A payment channel can be thought of as a full bottle of water: in order to pour something in one first has to pour something out.
Each channel implicitly contains a reserve which is unspendable and typically takes about 2% of the channel’s capacity. You must spend an amount matching that reserve to make receiving possible. Unspendable channel reserve is the reason you see a negative receive limit when a new channel is full. It indicates how much you need to spend before anything can be received through the channel.
Every payment request is disposable, they can’t be fulfilled twice. So you will need to issue a new individual payment request for every incoming payment you wish to receive.
Wallet needs to be online in order to receive off-chain funds.
Next: Recovering lost balance