"DM me GUIDE and I will send it over." It is an easy call to action for a caption or a Story, and Respond to all DMs is the instant automation that keeps the promise.
This is the quick version with one keyword list and one reply. If you want branching, delays or Google Sheets, build it in Flow Builder instead: Use DM keywords in Flow Builder.
Create the automation
Go to Automations, click New Automation and choose Respond to all DMs.
Under Setup Keyword, type the word people will send and press Enter. Add a few spellings if your audience is likely to vary it, for example guide and guide please.
Under Send a DM, write the reply and add your link button or other blocks. See Multi-Message DM Automation for what you can include.
Click Go Live.
Keyword matching is not case sensitive, so GUIDE and guide both work. Unlike the comment trigger, this template has no Any keyword switch: you always list the words you want to catch.
Advanced options
Scroll to Advanced Automations for the same extras as Comment to DM:
Opening Message sends a "tap to get it" message before the reply.
Ask to follow before sending DM asks non-followers to follow first. Needs Opening Message. Setup on the Zorcha blog.
Collect Email DM asks for an email before sending the link (Pro).
Follow Up to Re-Engage sends one reminder if they do not tap the button. Pro plan, needs Opening Message. See the follow-up guide on the Zorcha blog.
Test it
From another Instagram account, send your keyword as a DM and check the reply arrives. Then send an unrelated message and confirm nothing is sent. If the reply does not come, check the automation is live, the keyword is spelled the way you sent it, and look at Account Safety in case sending is paused.