A coin nearly impossible to identify

It's worth a try, I guess. Can anyone see anything I missed with this coin? All I can see is a "REX" on one side.
It is silver, it weights 0.74, and has a diameter of 16-17.2mm. Thank you in advance for trying. :)

If you rotate 180 degrees the second image - so REX is lower left -
does it then look like there is a crown at the top?

Added other lettering as a guess ...

Yes, I can just about make out a crown at the top. On the rev. I see BO not IO. Many thanks. Could it be Hungarian or English?

Silver
16-17.2mm - though originally larger presumably
Both sides within inner circle

Second side:
REX lower left
Crown at top which intersects with circle

Something like this ...
https://en.numista.com/catalogue/pieces137970.html




Just a wild guess, especially lettering. The crown is wrong size, and so on. But maybe ...

Just seen your reply; I looked again and I see RO instead of BO lettering. Maybe.

Try this:
https://en.numista.com/catalogue/pieces85632.html

Seems that REX, O and crown fit.

Thank you so much, ZacUK and bdino! I really appreciate your help.