Once you have added a Passkey on MPChat, you have three faster ways to sign in: enter your account and let your local Passkey verify, scan a cross-device QR from another phone, or skip typing entirely with one-tap "Continue with Passkey". This article explains all three flows, when each one shows up, and what every error message means.

Sign in to MPChat with a Passkey

Passkey login replaces the SMS / email code or password step you used to see right after entering your account. The legacy code-based login still works in case your Passkey is unavailable — pick the flow that fits your situation.

Flow A — Same-device Passkey login (most common)

On the MPChat sign-in screen, enter your account (phone number or email).
Tap Sign in. MPChat checks the server: if this account has a Passkey, the system Passkey sheet pops up.
Confirm with Face ID, Touch ID, or your device PIN — that is the entire verification.

This is one continuous step (no separate "(1/2)" indicator) — once verified, you go straight into MPChat. If you tap Switch verification method on the Passkey sheet, MPChat falls back to SMS / email code or password login.

Flow B — Cross-device Passkey login (use another phone's Passkey)

If you are signing in on a phone where you have not stored your Passkey (e.g. your spouse's tablet, a friend's borrowed phone), the system sheet offers Use a passkey on a different device. The flow:

Tap that option on the device you want to sign in on.
The system shows a QR code.
Open the camera on the phone that does have your MPChat Passkey, point it at the QR, and confirm with Face ID / fingerprint / PIN over there.
The first device automatically completes sign-in.

This works because Passkey assertion is signed on the trusted phone but transmitted via Bluetooth + cloud relay; nothing about your Passkey is copied to the borrowed device.

Flow C — One-tap "Continue with Passkey" (no account typing)

On the sign-in screen, the bottom of the form has Continue with Passkey. Tap it and the OS shows the Passkey sheet directly — no need to type your phone number or email first.

If your phone has multiple MPChat Passkeys (rare — typically a family-shared device), the OS asks which account to use.
Once you confirm, the corresponding MPChat account is signed in.
You can also tap Use a passkey on a different device here to fall back to Flow B.

If the Passkey check fails

MPChat shows a single error dialog covering most failure types: "Passkey verification failed. Please try again or switch the verification method." Tap Got it to dismiss. Common causes:

You closed the system sheet by mistake → just retry.
Face ID / Touch ID failed several times in a row → wait a few seconds and retry, or fall back to device PIN.
The cross-device QR scan timed out → tap Use a passkey on a different device again to regenerate the code.
The other phone's Passkey is for a different MPChat account → make sure both devices are pointing at the same account.

Special errors during one-tap login

"Account does not exist or Passkey has been removed" — the Passkey on this device is stale (the account was deleted, or the Passkey was reset). See How to reset your Passkey.
"No Passkey for MPChat is stored on this device" — there is no MPChat Passkey on this phone yet. Sign in with phone / email + code first, then add a Passkey from Security Center.

Effect on 2FA

Login Passkey verification is independent of MPChat's account-level 2FA. If you have 2FA enabled for sensitive operations, those flows continue to require their second factor (see Verify with Passkey for fund flows).

Newly bound Passkey vs reset Passkey

To prevent account-takeover via a stolen phone, MPChat applies a 24-hour withdrawal cool-down only when you reset a Passkey via face liveness. First-time Passkey binding does not trigger the 24-hour cool-down.