We have created a basic custom theme for WordPress. When trying to access Appearance > Customize from the backend we receive an internal error 500. I have checked the error logs and cannot find anything relating to this.
The website is working fine, the theme is working fine as expected, just accessing the customize section.
Do we need to include anything specific in the functions theme file to be allowed to access this section? Does a part of the theme have to be customizable in some way? I have tried various searches for this, although the basic 500 errors seem to come up a lot. I.e. htaccess, plugin issues.