inlineEnrollmentFactorsRequired, at least one factor should be available at each level as per documentation (1).
So, if a user needs to enroll to MobileOTP with SMSOTP:1, EMAILOTP:1, then having only a mobile phone or only a mail address registered, or both, it should work.
Currently, if the user has only a mobile phone or email, then the transaction results in AUTH_DENIED.
There's a problem in the VIP Authentication Hub code, for which a patch is available now in the VIP Authentication Hub 2.2.3 (DE589230) (2).
Upgrade VIP Authentication Hub to 2.2.3 to benefit from this fix.