You can configure and connect Teradek to Castr by adding a Custom RTMP option in Teradek.
Click the gear button on top right
Click Add Destination
Choose Custom RTMP
Paste the Ingest server and stream key provided by Castr in Custom RTMP setup page.
Username and password is not required and you can leave the fields empty.
Click Done and go back to the main page of the app
You can now ready to Go live and stream to Castr Ingest Points