Following is useful for taxonomy field type. There is no option in ACF to set min max for taxonomy multi-select.
add_filter('acf/validate_value/name=select_product_category', 'my_acf_validate_value', 10, 4); function my_acf_validate_value( $valid, $value, $field, $input ){ if( !$valid ) { return $valid; } if(sizeof($value) > 3) { $valid = 'You can only select 3 terms'; } else { $valid = true; } return $valid; }