Why isn't a customer getting texts?

First, Tools → Connected Services → Your Text Number: with no number of your own, automatic texts are not sent, and once connected, Check my setup shows whether replies reach you and whether your carrier (A2P 10DLC) registration is approved — carriers block unregistered business texts. A customer who replied STOP gets no texts until they reply START, and one who left the text-consent box unticked at checkout gets none either. Automatic texts also wait for daytime on the customer's own clock; if we can't tell their time zone, confirm it on their page. Also check the number on file is a mobile number.