Hey there TLLLP,
To clarify, does this only happen when accessing the link via social media, or are you able to access the link through a web browser instead? If the link does not populate as expected from the web browser along with social media, it sounds like the link might be the issue.
If the link also does not load in a web browser, you can try the troubleshooting steps found here:
Clear website data
You can clear website data occasionally to improve Safari performance.
1. Go to Settings > Safari.
2. Tap Clear History and Website Data.
3. Tap Clear History and Data to confirm.
If Safari isn't loading websites or quits on your iPhone, iPad, or iPod touch - Apple Support
You might also be able to find help with Facebook links on their support page here: Troubleshoot Link Failures | Meta Business Help Center
Take care!