If you’ve created the acf-json folder in the theme folder then is should be working unless there is a write permission problem.
If you are using a child theme then that acf-json folder must be in the child theme folder. If you want the acf-json folder to be in the parent theme then what you need to do is have one site that uses the parent theme where you make changes while all other sites use the child theme and in the child theme you add a json load point to load groups from the parent theme.
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