Prepaid or "Pay as you go" plans sometimes block shortcodes to prevent unexpected balance depletion.
Here’s a concise, practical guide to unblock shortcode texting for T-Mobile Work (T-Mobile for Business): how to unblock shortcode texting t mobile work
Try texting the word "ALLOW" to the specific shortcode you are trying to reach; some services require this manual opt-in. Prepaid or "Pay as you go" plans sometimes