I am getting the same error while doing an http post for creating a global index request.
Here's my service configuration
<Search>
<add key="SearchEngineUrl" value="https://vishalazuresearchservice.search.windows.net"></add>
<add key="SearchEngineName" value="AZURESEARCH"></add>
<add key="SearchServiceURL" value="http://localhost:8088/DuckCreek"></add>
<add key="SearchServiceVersion" value="2020-06-30"></add>
<add key="SearchServiceKey" value="E2FB03B744EA4A6896A10BE6AA745FED"></add>
<add key="SearchTenant" value="policy"></add>
<add key="SearchWorkflowManuscript" value="Carrier_SearchWorkflow_Data_1_0_0_0"></add>
<add key="SearchInterfaceManuscript" value="Carrier_SearchInterface_Data_1_0_0_0"></add>
<add key="SearchConfigurationManuscript" value="Carrier_SearchConfiguration_Data_1_0_0_0"></add>
<add key="IndexDataForSearch" value="True"></add>
</Search>