Plan is up to date, have cell service, but messages not being sent. Receiving messages just fine.
Make sure you don't have a picture message waiting to be sent because you don't have your data turned on. Turn your data on and wait for a couple minutes and then if your have a removable battery take it and your SIM Card out for a minute or so then replace them and try it again. If you don't have a removable battery then press and hold the power button until the device shuts off and continue holding it untiltthe device turns back on (power cycle the device) thenttry texting again.