FYI, I reached out to support about this and was told, "It looks like Credo is either using the Sprint or Verizon network so users should be able to subscribe to our text notifications selecting one of those two options. I recommend sending test messages to the user's mobile number using the Sprint format ##########@messaging.sprintpcs.com and the Verizon format ##########@vtext.com. If they receive one of those messages, they should select that provider when subscribing."