string-to-buff

there is no such thing in clarity string-to-buff

You can use to-consensus-buff?
And then remove the type and length bytes at the beginning

(define-read-only (ascii-to-buff (in (string-ascii 100)))
(default-to 0x (match (to-consensus-buff? in) buff (slice? buff u5 (len buff)) none))
)

https://github.com/Rapha-btc/Smart-Wallet/blob/4228dff5512e9d35b5c739b6f1ad7f65649fb226/contracts/passkey-smart-wallet.clar