Cannot load site on any device connected to my wifi

I am not that computer literate so please bear with me. I have numeroud devices connected to my wifi, I was able to connect to a gift site (mygiftcardsplus) and then was not able to from any of my devices that were connected to my home wifi. This happened suddenly a few months back. I can connect via my phone data to load the site. To be sure it was my wifi I had a relative bring over her device and try loading it connected to my wifi and she could not either. It works on her home wifi before and after. I have reset my router and am not sure how to go about fixing the issue. Thank you in advance for your time and any advice.