Documentation clarification: payment uniqueness

[roqqit]

According to the documentation here: https://docs.paybutton.org/#/?id=disable-payment-id

disable-payment-id is false by default but random-satoshis is also false by default. These are not in conflict, but the documentation implies that these fulfill similar purposes to ensure users do not trigger payment for each other. Please clarify in what case(s) we should use one or the other. A quick reading of the code suggests paymentId is the preferred method, but does random-satoshis provide a benefit? Is there peace of mind for larger or more frequent transactions?

Any clarification you can provide on these points in the docs would be helpful thanks

[Klakurka]

We'll add clarification. tl;dr is that XEC has good support for OP_RETURN in its major wallets whereas BCH does not, so paymentId (which currently only appears in the OP_RETURN) cannot be relied on for all payments across all chains.

[roqqit]

Understood. so if my math is correct, on BCH I would need to enable random-satoshis. with a max of 4 random digits, I'm quite limited to the number of concurrent users paying the same base value that I can support before a collision occurs.

probability of collision: 1 − e^(−k(k−1) / 2N)
N = 9999

probabilities given k concurrent users:
k = 100 : 39%
k = 50 : 11.5%
k = 30 : 4.3%
k = 20 : 1.9%
k = 10 : 0.4%

it seems paymentId is certainly preferred so long as it is supported