How do I get texting to work on a Verizon Samsung Galaxy S4 with T-Mobile service?

I just got this phone about a month ago and I am not able to send any text messages but yet, I can receive them. MMS, data, and calling works pretty good too. MMS didn't work at first until I had to change my APN settings. Is there a way to fix this?

Does this problem have something to do with the software version? It's 5.0.1 (lollipop)

Texting no longer works after AICP update to Lollipop

I have a HTC One m7 which I bought about 6 months ago on eBay. It came rooted and running AICP.

I do not really understand how rooting or flashing works so I just kept it as it was. I did not install any updates and I wasn't sure what they would do or whether I needed to do anything else to have them work.
Just yesterday, I installed the latest update after it appeared in a notification. It downloaded, installed, rebooted and seems to have generally worked, the phone now looks like Lollipop rather than Kitkat etc.
The AICP OTA gives system info as:
ROM version: 10.0 NIGHTLY0 (20151007)
Google apps version 0.0 (0)

With help from Zelendel I also installed GApps successfully.

I am not receiving text messages (I'm using the 'Messaging' app) and when I press to send a text message, the message does not appear on the conversation and no text is sent.

es0tericcha0s suggested that I may need to update the firmware, but that I would have to revert my phone to stock in order to do this.

Is there an easier way to get my texting to work? I am a noob when it comes to all things rooting so forgive me for my ignorance.

I have hboot 1.57 and S-off.