This is how TextWork screens started, before any ATS or job board was connected. Put a line like “Text JOB XYZ to (555) 010-4477 to apply” on a flyer, a job post, or a QR code.
TextWork matches the phrase, adds the person as a contact if they are new, and starts the script attached to that code. There is no JOIN prefix. The phrase is the whole code, and spaces and hyphens count the same.
Create one under Company Settings, on the Team tab. Leave the phrase blank to generate one, or type your own. You can also cap how many times it is used.
Someone who texts your number without a code gets one reply asking for it, at most once a day.
How to use it is in How conversations begin.