Straight talk Galaxy s8 using Verizon byop can't change apn settings?

[Android Central Question]

I have a galaxy s8 that was purchased from straight talk. The phone is unlocked. Yesterday I bought a Verizon byop kit for prepaid and I can't send or receive picture messages. I go to change my apn settings and they are all grey and cant be changed. I put in a att Sim card and was able to change my settings but once I put my vzw one back in it deleted it and out me back on the one that comes with the Sim. Called Verizon and Samsung and nobody knows how to fix it. Verizon told me to use text free or another app
Anybody know a fix? How I can maybe force a apn setting change? I'm not as savvy as you guys but I do know my fair share.