My phone is an unlocked verizon phone using a t-mobile sim card. Why can't it send texts?

[AC Question]

My dad’s old work phone is verizon, but our carrier at home is t-mobile, so I have a t-mobile sim card in it. I fixed the apn settings to t-mobile already. I can use cellular data, receive texts and calls and answer them with no problems, but I cannot send texts without attaching a picture to it.

 

[BattleSwine]

What is the make, model, and OS version of phone? What app are you using SMS?