If you've implemented a proxy server in front of the Digipass S3 API Server which uses a different front-end URL (in the browser) for REST calls or a different proxy instead of the API Server, then you need to configure a regular expression so the Digipass S3 App SDK can verify the endpoints. For more information, see Implementing a Proxy Server in the Web Developer Guide.
If your proxy server has specific rules for its URL, then you may need to adjust your API Server configuration. See API Server properties for the different settings you can use to further configure the API server.