Welcome to the forums!
Based on the information that you've provided it's hard to say.
Do you have a good cellular signal (3 or more bars)?
Are you sending SMS (only requires a cellular signal) or MMS (requires a Mobile data connection)?
Does this happen for everyone or just specific contacts?
Do you receive TMs ok?
Did the problem just start (could be a problem with your carrier) or has it always been this way?
Sent from my rooted, debloated, deodexed Sinclair ZX-80 running CM -0.001 using Tapatalk Pro