Why does HN change my URL to a bootstrap URL?

I submitted my project to Show HN. But after submitting, the URL changes to a bootstrap link.

A screenshot here: https://twitter.com/JorisFalter/status/1571710284724830210/photo/1

The link was https://www.samedayblocker.com and changed to https://getbootstrap.com/docs/5.1/examples/heroes/

Thanks for your suggestions