I have fixed this problem by adding the dynamic featured image meta key into allowed types for JSON API with the filter ‘rest_api_allowed_public_metadata’. I used the code below.
function custom_rest_api_allowed_public_metadata( $allowed_meta_keys )
{
// only run for REST API requests
if ( ! defined( 'REST_API_REQUEST' ) || ! REST_API_REQUEST )
return $allowed_meta_keys;
$allowed_meta_keys[] = 'dfiFeatured';
return $allowed_meta_keys;
}
add_filter( 'rest_api_allowed_public_metadata', 'custom_rest_api_allowed_public_metadata' );