user65564: If A and B have a Lightning Network channel，it was opened with a funding transaction (say, 1BTC from both sides for 2BTC total).  After A has spent some time transacting with B, the balance of the balance of the channel will be spent and then the channel will be closed with a confirmation transaction. Why doesn't the Lightning Network support additional funding transactions within this existing channel so that A and B can continue use this channel for transactions?

user73398: The total capacity of a channel cannot be increased since the funds are held in a single UTXO (unspent transaction output). What can be done, however, is to rebalance the channel from within the Lightning Network itself, so A can use it again.
Let's assume the balance of the channel is now 0 BTC for A and 2 BTC for B, so A cannot send payments through the channel anymore. That makes A want to fund the channel so he can spend more.
A can do this by asking a payment to be sent to him through LN that will effectively re-balance the channel to (say) 1 BTC for A and 1 BTC for B. This funding payment needs to originate from another Lightning node, for instance a Lightning-enabled exchange where A pays fiat (or other crypto) and gets 1 BTC sent to his Lightning node.

user48884: Any additional funding transactions would not be covered by older commitment transactions which can result in the loss of funds. Older commitment transactions will not contain inputs that spend from the new funding transaction. The funds sent in the second funding transaction require B to sign a spending transaction, and if B refuses, then A has no way to get those funds back should an older commitment transaction be broadcast.

65564: <p>If A and B have a Lightning Network channel，it was opened with a funding transaction (say, 1BTC from both sides for 2BTC total).  After A has spent some time transacting with B, the balance of the balance of the channel will be spent and then the channel will be closed with a confirmation transaction. Why doesn't the Lightning Network support additional funding transactions within this existing channel so that A and B can continue use this channel for transactions?</p>
 73398: <p>The total <strong>capacity</strong> of a channel cannot be increased since the funds are held in a single UTXO (unspent transaction output). What can be done, however, is to rebalance the channel from within the Lightning Network itself, so A can use it again.</p>

<p>Let's assume the balance of the channel is now <code>0 BTC</code> for <strong>A</strong> and <code>2 BTC</code> for <strong>B</strong>, so <strong>A</strong> cannot send payments through the channel anymore. That makes <strong>A</strong> want to fund the channel so he can spend more.</p>

<p><strong>A</strong> can do this by asking a payment to be sent to him through LN that will effectively re-balance the channel to (say) <code>1 BTC</code> for <strong>A</strong> and <code>1 BTC</code> for <strong>B</strong>. This funding payment needs to originate from another Lightning node, for instance a Lightning-enabled exchange where <strong>A</strong> pays fiat (or other crypto) and gets <code>1 BTC</code> sent to his Lightning node.</p>
 48884: <p>Any additional funding transactions would not be covered by older commitment transactions which can result in the loss of funds. Older commitment transactions will not contain inputs that spend from the new funding transaction. The funds sent in the second funding transaction require B to sign a spending transaction, and if B refuses, then A has no way to get those funds back should an older commitment transaction be broadcast.</p>
