I did manage to get results @SAS Latlas by following the Create Bing Search resource through Azure Marketplace referenced in this quick start. However, I did not Create a custom search instance. After creating the resource in Azure, I sent the request through Postman that generated the attached response. See if that works for you. If you did happen to create a custom search instance, please comment down below with how you went about creating it.
Ocp-Apim-Subscription-Key was set to the Key 1 in my Bing Custom Search Azure resource.