Accessing API Management API from Excel using organizational account

In our organization we have some people that uses Excel to access our APIs. We would like the APIs to be exposed by API Management and to be authenticated using Azure Active Directory.

In excel this can be achieved by using an "Organizational account", but currently I get the message "We couldn't authenticate with the credentials provided. Please try again"

I have followed this guide in order to set up an Active Directory Registered application and configured API Management accordingly.

One additional step I have done is to add the "WWW-Authenticate" header in following in API management configuration, in order to trigger Excel to do authentication against our AD tenant:

<policies>
<inbound>
    <base />
    <validate-jwt header-name="Authorization" failed-validation-httpcode="401" failed-validation-error-message="Unauthorized. Access token is missing or invalid.">
        <openid-config url="https://login.microsoftonline.com/<tenant-id>/v2.0/.well-known/openid-configuration" />
        <required-claims>
            <claim name="aud">
                <value>expected-aud</value>
            </claim>
        </required-claims>
    </validate-jwt>
</inbound>
<backend>
    <base />
</backend>
<outbound>
    <base />
</outbound>
<on-error>
    <choose>
        <when condition="@(context.Response.StatusCode == 401)">
            <set-header name="WWW-Authenticate" exists-action="override">
                <value>Bearer realm="<tenant-id>", error="invalid_token", error_description="Access Token missing or malformed.", authorization_uri="https://login.microsoftonline.com/<tenant-id>/oauth2/v2.0/authorize", client_id="<client-id>"</value>
            </set-header>
        </when>
    </choose>
    <base />
</on-error>

When looking at the HTTP requests in Fiddler, the a request made to login.microsoft.com actually retrieves a token. This is the body of the response:

{
    "token_type": "Bearer",
    "scope": "some-scope user_impersonation",
    "expires_in": "3599",
    "ext_expires_in": "3599",
    "expires_on": "1600932873",
    "not_before": "1600928973",
    "resource": "https://api-management-host",
    "access_token": "<access-token>",
    "refresh_token": "<refresh-token>",
    "id_token": "<id-token>"
}

But the following request to API management does not contain the token - the authorization header only has the keyword Bearer:

Authorization: Bearer

Anyone out there that have any experience with this scenario - or can help me solve this issue?