If a candidate has texted your short code and does not get a response, there can be a few issues to cause this.
1. Have candidate test if their carrier is blocking short codes in general. Have the candidate text HELP to 47272. If no response then their carrier plan is most likely blocking short codes.
2. Report the issue to firstname.lastname@example.org with the candidate cell number, and the general time they attempted to use your short code.