When API Gateway and Developer Portal are deployed on different machines, configuring Developer Portal as the destination fails with the following error message when I click the Test button, "The input url https://sawld01.cmcdev.be:18102/portal/rest/v1/providers?tenantId=default is not allowed as the host is in denied list. Contact administrator".

Resolution:

Using the REST API, update the Developer Portal's IP address in the API Gateway's whiteListedIPs /rest/apigateway/configurations/whiteListingIPs