Hey there jspicker,
Thanks for reaching out to the Apple Support Communities. To get started, does this issue occur when trying to send an iMessage (text bubble would be blue), or a SMS/MMS message (green text bubble)?
If this message appears when trying to send a SMS/MMS message, and based on the alert you're receiving, it's possible that the message may be blocked on your carriers end. If this is the case, we would recommend reaching out to your carrier to ensure that there are no issues on their end.
If the issue occurs when trying to send an iMessage, or your carrier has confirmed that there were no issues on their end, check out the steps in the following resource that can help troubleshoot the issue further: If you can't send or receive messages on your iPhone or iPad - Apple Support
If you have issues with Messages after you set up a new device
If you experience issues like conversations in Messages showing up as separate threads or sent messages appearing as green message bubbles instead of blue message bubbles when you set up a new device, update your settings using the following steps:
1. Update your device to the latest version of iOS or iPadOS if needed.
2. In the Settings app, tap Cellular. Make sure that your phone line is turned on. If you use multiple SIMs, make sure that the phone number you want to use is selected and turned on.
3. In the Settings app, tap Messages. Turn iMessage off and then back on.
4. Tap Send & Receive.
5. Tap the phone number that you want to use with Messages.
If you have issues when you try to receive a FaceTime call after you set up a new device, you can also update your FaceTime settings.
Keep us updated on the results after going through the steps above, and we'll continue from there.
Take care!
