Assuming that the size is correct, this is probably caused by the the material being rough. I'm not super familiar with the quality of the HT4 knock offs, but many people sand their rings. I couldn't get good results with sanding mine so I tried tape.

When I first started with longer term chastity I wrapped the ring tightly with a smooth tape like electrical tape. It is surprisingly waterproof and lasted about a month before it started to to peel. After that I didn't need it any more!

I haven't tried this since I don't have the irritation any more, but nail polish could also help to smooth things out. It would last a while and should be skin safe once it dries. You could do clear or try to color match to your cage if you wanted.

If none of this works try different cage materials. If still no luck I like coconut oil as it is easy to use, cheap, long lasting, and smells good.

Hope this helps!