Added note for bLIP 10 fields removed by #510

[ericpp]

The spec was changed when it was transferred over from the lightning repo and several unused or underused fields were removed (see #510). This PR adds a note listing the fields that were removed and links to the #510 for more info.

Some apps are still using these fields (particularly value_msat, see: https://reflex.livewire.io/apps) and it would be good to indicate in the spec that they should no longer be used

[ericpp]

And since value_msat is still widely used, maybe it should be re-added to the spec? It was removed since the invoice itself already contains the number of received msats.

[johnspurlock]

value_msat would be very useful to include in the spec (it's in the example!), as it can contain millisats (i don't think invoices can or at least do?) - millisats are useful to back into the total amount if you have a small split

and it's a great indication of "what the client meant to send", to be sanity checked against what was actually received

also, as you say, already being sent by many

[johnspurlock]

this was my only recommended note for whoever is in charge of the spec over in https://reflex.livewire.io/apps

[ericpp]

@johnspurlock Invoices do contain both sat and msat totals:
e.g. lncli output

"value": "34",
"value_msat": "34000",
...
"amt_paid": "34000",
"amt_paid_sat": "34",
"amt_paid_msat": "34000",
...
"htlcs": [
    {
        ...
        "amt_msat": "34000",
    }
]

value_msat might be useful since it contains the original split value before any lightning routing fees are taken out. I think this can still be derived from the HTLCs in the invoice, but it might be more convenient to get it from the TLV. Actually, lightning routing fees are added to the payment amount rather than taken from the payment amount. The split total should be the same as the total listed on the invoice.

On the other hand, getting it from the invoice is better for reporting actual received msat totals, since TLVs can be easily spoofed. It's easy to send a 1 sat payment with a TLV that says I sent a 1M sat payment.

[samsethi]

Thanks to @johnspurlock we added both value_msat and value_msat_total to the Alby Dashboard. Are we missing anything else John?