[bug]: Unable to pay AMP invoice with `amp` flag set to true

[saubyk]

Background

Trying to pay an AMP invoice with payinvoice command and amp flag set to true throws an error the AMP flag (--amp or SendPaymentRequest.Amp) must be set to pay an AMP invoice

./lncli -n=regtest payinvoice lnbcrt1u1pnr0n3cpp5zy9t58wttquf8dwxm8dymt9xxe27r003nv4w4py5unu768gnhajqdq423jhxarfdenjqctdwqsrycqzzsxqyjw5qsp52zuqjsgrn0k4g7ka5zthszjcvydxcfgl6hvjqzvzkkfa20ff3djq9q8pqqqsgq4w8ye3jxl30v6ez8c9h2mwyn65flu2qgdsclxkkh2cm5umsq6vezqf34sjx8jz4yc3m3h7uuuzgy95r5xkvt9pawpalnyv6hg3lzszspxkxkmw --amp=1
Payment hash: 110aba1dcb583893b5c6d9da4daca63655e1bdf19b2aea8494e4f9ed1d13bf64
Description: Testing amp 2
Amount (in satoshis): 100
Fee limit (in satoshis): 100
Destination: 02f31d2b3830e8afaf8621044460fa1ad6165aa0071601f8b26168a985c4d1cc08
Confirm payment (yes/no): yes
[lncli] rpc error: code = Unknown desc = the AMP flag (--amp or SendPaymentRequest.Amp) must be set to pay an AMP invoice

 ./lncli -n=regtest decodepayreq lnbcrt1u1pnr0n3cpp5zy9t58wttquf8dwxm8dymt9xxe27r003nv4w4py5unu768gnhajqdq423jhxarfdenjqctdwqsrycqzzsxqyjw5qsp52zuqjsgrn0k4g7ka5zthszjcvydxcfgl6hvjqzvzkkfa20ff3djq9q8pqqqsgq4w8ye3jxl30v6ez8c9h2mwyn65flu2qgdsclxkkh2cm5umsq6vezqf34sjx8jz4yc3m3h7uuuzgy95r5xkvt9pawpalnyv6hg3lzszspxkxkmw
{
    "destination": "02f31d2b3830e8afaf8621044460fa1ad6165aa0071601f8b26168a985c4d1cc08",
    "payment_hash": "110aba1dcb583893b5c6d9da4daca63655e1bdf19b2aea8494e4f9ed1d13bf64",
    "num_satoshis": "100",
    "timestamp": "1714933304",
    "expiry": "604800",
    "description": "Testing amp 2",
    "description_hash": "",
    "fallback_addr": "",
    "cltv_expiry": "80",
    "route_hints": [],
    "payment_addr": "50b80941039bed547adda097780a58611a6c251fd5d9200982b593d53d298b64",
    "num_msat": "100000",
    "features": {
        "8": {
            "name": "tlv-onion",
            "is_required": true,
            "is_known": true
        },
        "14": {
            "name": "payment-addr",
            "is_required": true,
            "is_known": true
        },
        "30": {
            "name": "amp",
            "is_required": true,
            "is_known": true
        }
    }
}

Your environment

• version of lnd - 0.18.0-beta.rc1

Steps to reproduce

• Generate an AMP invoice
• Attempt to pay the invoice with the payinvoice command and amp flag set to true

Expected behaviour

Should be able to pay the invoice if the amp flag is set to true

Actual behaviour

Throws a rpc error