I can no longer send messages from my iPad after installing 17

I figured this out. The first thing to do is to make sure you are signed into the same AppleID as you are signed into your phone. You might think you have only one AppleID, but if you have had an account for a long time, you may have multiple ways to sign into the account with the same password.

To check this, go to your settings on the iPhone. Then navigate to Messages, and click Send & Receive. At the bottom of the list of addresses is the AppleID that your phone is logged into. Now check your iPad login the same way.

Once you are logged into the same AppleID, check the name of your iPad. To do this, go to Settings->General->About.

Now that you are logged into the same AppleID and know the name of your iPad, go to your iPhone Settings->Messages->Text Forwarding. The name of you iPad (and some of your other devices) should show. Make sure this is set to on (green dot).

This should fix it.

I’ve had the same issue with a brand new iPad. After ios 17, only some of my message threads work, and none of the one time passkey messages work. This makes 2-factor authentication inconvenient. I have turned off iMessages, backed up, turned the iMessage back on, rebooted, and reset the whole device multiple times, but the same failures happen on my iPad. My phone messages (on the latest os) work fine.