This is just a guess .. If you ard using the stock app that came with the Android phone ..
Tap on the app ..
Then in the top right corner you will see threr dots ..
Tap on them ..
Tap on settings
Tap on advance .. and scroll down.
Tap on .. Get SMS delivery reports ..
Restart your phone ..
Hopefully that should sort it !
Sorry I use an MIUI platform.. therefore I can't guess as to exactly what you see on your screen.
The answer will be in the app settings and you are looking for 'SMS delivery report' or something worded like that. You will just have to enable it.