Another one adding my voice here. PayPal is the only website I've come across that accepts WebAuthn but only ollows you to register one key, and requires TOTP as backup. I've got multiple Yubikeys, exactly so that the spare ones are backups. Requiring TOTP as backup basically means you migth as well not support security keys. I decided to just use a TOTP app and not to register my security keys with Paypal.
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