Possible values: 'CHAR', 'NUMERIC', 'ARRAY
Used with meta_key fields to specify the type of data stored by the meta_key. Necessary in order to perform proper comparison operations (=, <, >, BETWEEN, etc). Defaults to ‘CHAR’.
Note: When attempting to search meta_keys created using the Advanced Custom Fields plugin, you may need to use the special value ‘ARRAY<CHAR>’. Some multi-value ACF fields (select, checkbox, etc.) store their values as arrays in the database, and using ‘ARRAY<CHAR>’ will allow you to search them properly. In these cases should also set ‘compare‘ => ‘LIKE’.