We'd love to get your device up and running again! There are a few additional troubleshooting steps we can take, which may fix the problem. For starters, is your phone up to date with the latest operating system?
Another step would be to clear your cache data. Simply go to Settings > Storage, and you’ll be able to see just how much space is being used by the partition under Cached Data. To delete the data: Tap Cached Data, and tap Okay if there’s a confirmation box.
Lastly, you can start your phone in safe mode. First, turn the phone off. Press and hold the Power/Lock key for one or two seconds to turn on the device. Let go of the power button. When the Animated Samsung logo displays (it should be the second Samsung logo that you see), press and hold the Volume down key. When the lock screen displays, the words "Safe mode" will be shown in the lower-left corner of the screen. If you are able to send messages in safe mode, then this means the problem is being caused by a 3rd party app.
Please give these a try, and let us know if any of them work out for you. You can also visit our Galaxy S8+ support page for more information about your device.
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