Merchant initiated transactions are those that are triggered on renewals and one time charges. According to SCA, most off-session payments that are Merchant Initiated Transactions will be treated as exemptions. However there is a minor possibility that some transactions are made to go through 3DS, invariably. To handle such cases, we have designed a fallback mechanism.
We are ramping up our dunning and email notification settings to notify existing customers about the 3DS authentication. Using the email notification, they would be able to complete the entire process with ease.
More details on this will be updated soon.