And is there an app or service in existence currently using OTPs "properly", as you say? OTPs are extremely onerous, if not impossible to implement properly in

And is there an app or service in existence currently using OTPs "properly", as you say? OTPs are extremely onerous, if not impossible to implement properly in real life in a way that scales. Hence why nobody uses them (instead people use RSA/ECC/AES/etc).