Hi there Lallie94,
We understand that you are unable to send GIFs in the Messages app on your iPhone. We’d be happy to help.
To start, does this happen with every contact you try to send a GIF to or only with certain contacts? Can you receive GIFs without issue?
Send and save GIFs on your iPhone, iPad, or iPod touch
Also, let’s update your iPhone to the latest version of iOS, 15.3, using this article:
Update your iPhone, iPad, or iPod touch
If this continues after updating and with multiple contacts, please provide more details on what happens when you try to send a GIF and if you are getting an error message of some kind.
Cheers!