Apologies if this is in the wrong area.

I expressed to my partner something I enjoy receiving but he won't try it and i tried to explain why I enjoyed it.

Sometimes it comes up casually. He makes a joke similar to what I'd like to do, so I mention itll be fun. His reaction is negative.

How do I talk to my partner about trying this kink out? (it's not dangerous or harmful.)
We have talked about our boundaries of 100% off limits. This isnt one of them.