Paying an external lightning address

[grunch]

hi, I'm trying to pay a ln address using the recipient field, I'm doing it like this

curl --location 'https://mylndhubx.server/payinvoice' \
--header 'Content-Type: application/json' \
--header 'authorization: ey.....' \
--data-raw '{
    "recipient": "negrunch@ln.tips",
    "amount": "0.00000006"
}'

but all the time I'm getting this response

{
    "error": "ServerResponseTimeout"
}

I have 5000 sats on balance on this account, and I already paid a lightning invoice with this same endpoint using the payment_request field and it worked ok, am I doing something wrong? thanks