Why won’t my link port work?

I recently purchased a link cable so that I could trade Pokémon between my two game boy colors. I tried using the link cable and it only registers on one of them. The other gbc doesn’t recognize that there is a link cable attached. There isn’t a problem with the cable or with either game I checked with different ones. I think it may be an issue with the port but I’m not sure how to fix it.