Unfortunately this is no longer an option as Speechmatics is discontinuing their web portal (meaning the access to STT with API key will no longer be supported) from 30th of Sept 2020. See their deprecation notice for more details.
sign up to speechmatics at app.speechmatics.com/
In the navigation bar click Account
Get User ID and API Auth Token
API Auth Token
copy and paste into the app's settings under Speechmatics.