How long is the card nonce valid for after it’s generated via Square Payment form?
Hey @lukel welcome to the forums!
They expire in 24 hours (https://developer.squareup.com/docs/api/paymentform#cardnonceresponsereceived):
Tokenized payment card information. The nonce is a string representing the nonce that was created or null if an error occurred. Nonce values expire after 24 hours .
Can I assume that once the nonce is used for a payment, it will not longer be valid?
Yes, that is correct.