Had the same problem for unknown reason. Tried to uninstall other plugins but no luck.
Problem is from the URL to wp-json which contains a double slash (//):
/wp-json/njt-fbv/v1//get-folders?sort=
Finally made it work again doing this in functions.php:
function my_filebird_json_url( $string ) {
// /wp-json/njt-fbv/v1//get-folders?sort=
// /wp-json/njt-fbv/v1/get-folders?sort=
$string = str_replace(‘/v1/’, ‘/v1’, $string);
return $string;
}
add_filter( ‘filebird_json_url’, ‘my_filebird_json_url’, 10, 1 );