I can no longer send or reply to an sms text message to an iphone on the at&t network

[AC Question]

Using the standard android messenger app on a Nexus 5x phone on Verizon. Got a text from an iphone on the AT&T network and was not able to reply to the message. Tried to send a new SMS text message to the iphone on the AT&T network but that wouldn't go either. I can however send an MMS message to the iphone on the AT&T network. I can send an SMS message to another iphone fine that is on the Verizon network. This problem just seems to have started in the last week. Any ideas?