Enroll MFA OTP on SPA

Following the procedure to enroll and challenge OTP authenticator, we have an error during the enrollment :

Grant type 'http://auth0.com/oauth/grant-type/mfa-otp' not allowed for the client.

My Request :

URL : https://login.XXXXX.XXXXX/oauth/token
data : {
client_id: <MY CLIENT ID>
mfa_token: <MY_MFA_TOKEN>
grant_type: http://auth0.com/oauth/grant-type/mfa-otp

My application config :

this message seems similar to this one but for MFA OTP.

Do you have any idea what I am missing ?