At this time it is not possible to use the Starling 2FA Radius Agent with applications that do not perform challenge / response.
The following ER has been raised so that the Starling 2FA Radius Agent can be used with legacy applications that do not perform challenge / response.
ER 114582: "Configure 2FA RADIUS Agent to automatically send push notification or OTP after primary authentication"
At the time of this writing, November 19th, 2019, there is no ETA on when this feature will be in Starling 2FA.
Please review the list of Resolved Issues and Enhancement Requests published within the product release notes to determine if this specific Change Request is included in an upcoming release. Release notes are available at support.oneidentity.com under the technical documentation section of our website. We do not guarantee that all Change Requests will be implemented in future releases. For more information on our Product Enhancements and Defects policy, please consult the One Identity Global Support Guide https://support.oneidentity.com/essentials/support-guide