This looks like a carrier-level issue, not the agent itself, since the same number works for some users and not others. I’d start by checking Twilio message logs for the failing numbers to confirm the inbound SMS is actually received. If it is, the next step is comparing carrier, 10DLC campaign rules, or prior STOP/opt-out flags for those users. Quick question: do the failing messages show up as “received” in Twilio, or are they missing entirely? @Red