A Lightning Network invoice is a request for payment issued by the receiver and contains all the information the sender needs to successfully execute the payment.
Usually it will be in the form of a QR code or an alphanumeric string that looks something like this:
* *CLTV Delta*: the delta to be used in the final HTLC in the path. Discussed in the earlier chapter on Routing.
* *Signature*: a digital signature by the invoice issuer. If anything in the invoice is changed, the signature check will fail and the invoice will no longer be valid. This prevents attackers tampering with invoices.
Even at an obscenely high Bitcoin value of $1m per Bitcoin, this would still allow the transfer of 1 US cent worth of value.
As many Lightning implementations track values to the thousandth of a Satoshi (i.e. one milli-satoshi), payments could conceivably be even smaller than this.
Technologies like CoinJoin and Pay-to-EndPoint can assist in giving Bitcoin users a greater degree of anonymity but cannot completely solve this problem.
In contrast, users of the Lightning Network are not aware of other users' payments and, since channels can be private, they may not even be aware of other users' channels.
Users are only aware of other users' payments insofar as they assist in routing payments; in this case they are unaware of both the source and the destination of the payment.
As such, the Lightning Network provides for strong use cases for anonymous purchases.
This would be of particular benefit to online stores and exchanges that accept Bitcoin as malicious attackers can monitor their addresses on the Bitcoin network to try and determine how much bitcoin the businesses owns
footnote:[One variant of this is called a "dust attack", whereby an attacker can send a very small amount of Bitcoin (called a "dust output") to an address it knows is owned by a store or exchange.
As Lightning wallets and Lightning invoices can be built directly into the games themselves, this completely bypasses the need for credit cards and the traditional financial system.
While Bitcoin may increase or decrease in value in terms of fiat currencies, it is an asset that does not offer a return in and off itself simply by holding it.
The amount of Bitcoin one holds remains constant, and actually decreases as one moves it around due to transaction fees.
Third-party services exist that provide interest on Bitcoin, but these services are in general not trustless.
Those wishing to earn a return on their Bitcoin holdings _trustlessly_ can do so by opening channels and routing payments in return for routing fees.
This way, users can earn a return (i.e. "interest") by locking their Bitcoin into channels and offering liquidity to other users wishing to transact on the Lightning Network.
Users doing so will need to pay the fees to open and close channels, as well as the cost of maintaining any hardware and network infrastructure to run a Lightning Node.
However, as channels can be left open indefinitely, they _could_ earn a profit as long as there are sufficient users of the Lightning Network such that their routing fees are in excess of their channel fees and maintenance costs over the long term.
This is trustless as users do not need to loan or send anyone their Bitcoin. Users only need to take on the efforts and risks of operating a Lightning node and storing Bitcoin in a hot wallet.
