Thank you for posting you query on Microsoft Q&A.
From above description I could see that you are trying to configure Transmit Security with Azure Active Directory B2C but are getting error while trying to signin to Transmit Security tenant.
Please do correct me in comments if this is not the case by responding in comments section.
The error you are getting is because your account is not recognized by BindID tenant.
As a Prerequisite I tired to sign-up for a BindID tenant.
While trying to access Get Started# BindID I found that it is a sandbox (dummy/test) portal.
- It did prompt me to enter email, followed by OTP, and later asked me to register my device.
- Kindly try to setup again with different browser or a different device.
- If the issue still persist kindly connect with BindID/Transmit Security support as Microsoft don't own BindID backend.
Thanks,
Akshay Kaushik