API Management - Set Backend Service as Operation Policy in Terraform - azure

Question

I'm creating an APIM in Azure using Terraform. So far I've been able to create the APIM instance, the API and an operation within the API. Because I want each operation for the API to point to an individual Logic App, my understanding is I cannot set this as an azurerm_api_management_backend and instead need to set it in the operation policy in XML.
This is what my operation policy looks like:
resource "azurerm_api_management_api_operation_policy" "apim1_ss_cmpcomplaints_api_dev_get_policy" {
api_name = azurerm_api_management_api.apim1_ss_api_dev.name
api_management_name = azurerm_api_management.test-apimManagement.name
resource_group_name = azurerm_resource_group.apimResourceGroup.name
operation_id = "get-complaints"
xml_content = <<XML
<policies>
<inbound>
<base />
<set-method id="apim-generated-policy">GET</set-method>
<set-backend-service id="apim-generated-policy" backend-id="/subscriptions/xxx/resourceGroups/hm-iac-msdn-neu-rg/providers/Microsoft.Logic/workflows/testLogicApp" />
</inbound>
<backend>
<base />
</backend>
<outbound>
<base />
</outbound>
<on-error>
<base />
</on-error>
</policies>
XML
}
I have created the Logic App and retrieved the resource ID from the Azure CLI and included it in the set-backend-service node. But despite getting the ID from the CLI, I am getting the following response:
│ Error: creating or updating API Operation Policy (Resource Group "apim-resource-group" / API Management Service "harry-test-apim" / API "test_api_dev" / Operation "get-complaints"): apimanagement.APIOperationPolicyClient#CreateOrUpdate: Failure responding to request: StatusCode=400 -- Original Error: autorest/azure: Service returned an error. Status=400 Code="ValidationError" Message="One or more fields contain incorrect values:" Details=[{"code":"ValidationError","message":"Error in element 'set-backend-service' on line 5, column 10: Backend with id '/subscriptions/xxx/resourceGroups/hm-iac-msdn-neu-rg/providers/Microsoft.Logic/workflows/testLogicApp' could not be found.","target":"set-backend-service"}]
I'd prefer to set this using the resource ID instead of using base-url.

Answer 1

The backend-id is different to the ARM id. It's not easy to find, so the solution is to generate the policy in the APIM front-end and then apply that in code afterwards.