Call REST API through order management extension

Summary:

I need to call a REST API via order management extension in order to check item availability for a specific item type.

Content (please ensure you mask any confidential information):

Hi,
i need to implement inside an "On Save" Extension, a REST API in order to check the Inventory Available to Reserve quantity for an item and eventually raise an error.
In the screenshot attached you can see all the setup and groovy script and OM error when try to save.

In the following official doc.:

https://docs.oracle.com/en/cloud/saas/supply-chain-and-manufacturing/25c/faiom/guidelines-for-calling-web-services-in-order-management.html#Process-Calls-to-Your-Web-Services