If you are experiencing green text on your iPhone while messaging, it may be due to an issue with iMessage. Here are a few steps you can take to fix the problem:
1. Make sure your iPhone is running the latest version of iOS (iOS 16). You can check for updates in the Settings app under General > Software Update.
2. Check to see if "Send as SMS" is enabled in your Messages settings. This will allow your iPhone to send text messages as a backup if iMessage isn't working properly. To enable this, go to Settings > Messages and toggle on "Send as SMS".
3. Reset your network settings. This will erase all saved Wi-Fi passwords and VPN settings, so be sure to have that information handy if you choose to do this. Go to Settings > General > Reset > Reset Network Settings.
4. Disable and re-enable iMessage. Go to Settings > Messages and toggle off "iMessage". Wait a few moments, then toggle it back on.
5. Contact Apple support. If none of the above steps work, it may be a more serious issue that requires professional assistance. You can contact Apple support through their website or by visiting an Apple store for help.