Added the error coverage for getHostedProUrl query

Author: Dinesh V B

src/guides/v2.3/graphql/queries/get-hosted-pro-url.md

@@ -50,3 +50,11 @@ The query returns the PayPal URL that enables the customer to sign in to PayPal
 Attribute | Data type | Description
 --- | --- | ---
 `secure_form_url` | String | Secure URL generated by PayPal
+
+## Errors
+
+Error | Description
+--- | ---
+`Could not find a cart with ID \"xxxxx\"` | The ID provided in the `cart_id` field is invalid or the cart does not exist for the customer.
+`The cart isn't active` | The cart with the specified cart ID is unavailable, because the items have been purchased and the cart ID becomes inactive.
+`Field HostedProUrlInput.cart_id of required type String! was not provided` | The value specified in the `HostedProUrlInput.cart_id` argument is empty.