It looks like CDC does not allow to capture subscriptions against pure Mobile OTP accounts. It appears as though subscriptions can only be used for Email Accounts.
The Customer may expecting to capture marketing Opt ins for out Mobile OTP Customers. They can no longer do this in an easy manner. There are other things they could potentially do (e.g. add a fake email address), however this is not a good solution especially if they also want to link Mobile OTP and Email Accounts and isn’t really a long term option. Other option is to create a complete Custom Solution for managing Communication Preferences.
Could you please let me know what can be done?