Also covering Stuckless payments and Boomerang payments

Redundant overpayments are LN payments split into parts where the spender sends a greater amount and more parts than necessary to pay the receiver’s invoice.

Even if some of the parts fail to arrive at the receiver’s node on the first try due to forwarding failures, enough of the other parts may arrive to allow the receiver to claim their invoiced amount. Protocol features prevent the receiver from claiming more than the invoiced amount. Compared to sending an exact amount, over paying initially can eliminate the latency of resending failed payments in most cases.

An overpayment requires a mechanism that prevents the receiver from claiming more than the invoiced amount. The simplest mechanism for implementing that is for the spender to not provide the receiver with all the information necessary to claim each payment part until the receiver indicates which payment parts have been received. The spender can then send the claim information for only the number of parts needed to claim the invoiced amount. A downside of this approach is that it requires an extra roundtrip of communication between the receiver and spender, which may be roughly equivalent to the time needed to handle one round of payment failures. By comparison, in the best case, an exact payment will complete on the first try. That means this type of redundant overpayments can, in most cases, put a low ceiling on the worst-case payment time at the cost of roughly doubling the best-case time it would take to send a non-overpayment.

Other mechanisms may be able to use cryptography to eliminate the roundtrip communication overhead, allowing overpayments to complete in the same best-case amount of time as non-overpayments. However, that approach may come with additional complexity and may require a significant number of forwarding nodes upgrade to support the new protocol before it can become widely used.

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