When the user initiates an SMS verification flow they will be prompted to enter the one-time code using the keyboard. It is important to do this to handle a situation where the user receives the SMS on a different device than the app is running on.

Then, if your app has requested SMS User Consent, an incoming SMS message containing a one-time code will be shown to the user with an option to to share the entire content of a single SMS message. This will only happen if your app has requested SMS User Consent and is running on the device that received the SMS message. It will never show messages that are sent from the user's contacts.

If the user chooses to provide the content of the SMS message to your app, the entire text of the SMS message will be shared. The user sees the SMS verification flow automatically complete.

For More Info please visit : https://developers.google.com/identity/sms-retriever/user-consent/overview