Every time I try to set a key for a locked container, it just says number of keys needed... I can't make a locked container with that

If you're on the web version, it seems that sometimes you need to set the number of keys needed, then look at another object and come back to the container. Then the right number of boxes will have appeared so that you can choose which objects are the keys.

No idea if the same thing happens in the desktop version.

Thanks!