Internal server error while running API in Azure API management

Question

I am following all the setps given in this document https://learn.microsoft.com/en-us/azure/api-management/authorizations-how-to-azure-ad, but while testing getting below error:

HTTP/1.1 500 Internal Server Error
content-length: 111
content-type: application/json
date: Mon, 14 Aug 2023 11:44:41 GMT
vary: Origin
{
"statusCode": 500,
"message": "Internal server error",
"activityId": "c561ed2b-8d50-4a50-802a-ef05d8840b0b"
}

and using below policy:

 <inbound>
        <base />
        <get-authorization-context provider-id="aad-01" authorization-id="aad-01" context-variable-name="auth-context" identity-type="managed" ignore-error="false" />
        <set-header name="authorization" exists-action="override">
            <value>20</value>
        </set-header>