I got "per_page is not of type integer" when I use the per_page parameter (to get product category list)

Question

According to the official documentation :

https://woocommerce.github.io/woocommerce-rest-api-docs/#list-all-product-categories

I should use per_page parameter to change the number of product category returned (default is 10).

But when I use it :

$endpoint = $store_url . '/wp-json/wc/v3/products/categories?per_page=50';

I got :

{"code":"rest_invalid_param","message":"Invalid parameter(s): per_page","data":{"status":400,"params":{"per_page":"per_page is not of type integer."},"details":{"per_page":{"code":"rest_invalid_type","message":"per_page is not of type integer.","data":{"param":"per_page"}}}}}

Any idea?

Thanks