@LeonBakker thank you for your question!
Within the MFA prompts there are 2 screens that may be the one you are seeing.
- mfa-begin-enroll-options (most likely it’s this one)
- mfa-login-options
If you are trying to use the Management API to customize the prompt/screen then it is expected that you’d receive and error when providing a screen name that doesn’t exist. The prompt screenshots and names are listed in the documentation link that you referenced in the accordions under Available Variables.
I hope this helps!