If a person messages in and it it not the correct keyword or is misspelled it will show up in your messages section.
This does happen sometimes and we always suggest that you try to make your keywords simple to avoid that. Try not doing two words or phrases as that can often be sent in wrong.
When you see that someone is intending to join one of your groups but what they texted in did not automatically put them in the correct group, it's easy to get them added to the group. Inside the conversation, simply click their name in green at the top of the page.
This will open their person record. From there you can choose the plus icon at the bottom right to add them to the desired group. Then any automatic workflow steps will begin at that point since they were just officially joined to the group.
If you need to adjust your keywords you can do that under the Groups tab, when editing the group details.