Here is a comment I just requested be added to the bottom of the register_setting() page.
If you plan to use your setting in the REST API, use both theCorey Salzano
admin_inithooks when calling
register_setting()instead of just
show_in_restargument is ineffective when hooked into
Someday, when my comment is approved, you’ll be able to see it on this page and save an hour or two of debugging time. If you can see my comment on this page, please let me know.