If you received a notification saying "Your SIM sent a text message," this may have come from Fi. We were making sure we properly updated your SIM card to the latest software version available by sending ourselves a text message with your SIM version number. This message was sent directly to Google Fi and there is no fee associated with this text message. There is no additional action needed from you. Please note: This notification may not show on all of your Fi devices.
In some cases, if you transferred your number from Google Voice you may have trouble verifying your number with WhatsApp. We're currently looking into the issue and we appreciate your patience.
If you experience this issue, please contact WhatsApp support and ask them to manually verify your number.