You need to enter a space or more between your message and a hashtag in order to use it as a link.

▼Correct example

There is a space between “Thank you” and “#”.

▼Wrong example

There is no space between “Thank you” and “#”.

How can I make sure that a hashtag is working as a link?

If you tap the “#” icon on the top left of the message screen, a space is automatically added. This way, you can make sure that your hashtag will function as a link.