Thank you for reaching out. Have you been able to message the contacts before the symptoms started happening? Did you recently switch from an iPhone to Samsung? If so and the same sim card was used sometimes this can happen when sending it to another iPhone user since the sim card is trying to use imessage and the Samsung device will not support it. If this is the case you will need to insert the sim card back into the iPhone and go to message settings and disable imessage. You can also go to your carrier and be issued a new sim card as well. If this is not the case then I would recommend doing the following.
Clear text messaging app data
There may be a bug within the text messaging app you’re using so the next good thing to do is to clear its data. This procedure will return the messaging app’s settings to their defaults and will erase all your text messages. If you want to keep them, try backing them up ahead of time.
You can do this by going to Settings > Clouds and accounts > Backup and restore > Back up data
Once backed up follow these steps to clear the app data.
Open Settings app.
Tap Apps.
Tap on More settings at the upper right (three-dot icon).
Select Show system apps.
Find and tap your app.
Tap Storage.
Tap Clear Data button.
Restart your S9 and check for the problem.
If your symptom still persist, I would then recommend resetting your network settings by following these steps.
From the Home screen, swipe up on an empty spot to open the Apps tray.
Tap General Management > Reset settings.
Tap Reset network settings.
If you have set up a PIN, enter it.
Tap Reset settings. Once complete a confirmation window will appear.
If the symptom still persists after performing these steps, I would recommend reaching out to your carrier for further assistance. If a new sim card and their assistance is unable to resolve this, I would perform a Factory reset on the device.
