There is not a get_rest_schema() method in the base class “acf_field”. The custom field template code was last updated 4 years ago. I assume that this function was added to the classes for each custom field after that.
You will need to create this method in your new class.
I do not know how this works. The only suggestion I can make is that you look at this method ACF’s custom field classes to see how it works to figure out what you need to do.
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