Consider using transactional message on ACS. As you don't need data to
be available within ACS to send transactional messaging. Once you have
all data sent through payload then message can be triggered. Also
detailed study required by looking at the use cases, remarketing
strategy etc when considering transactional messaging. Take a quick
glance of below documentation
link:https://docs.adobe.com/content/help/en/campaign-standard/using/communication-channels/transactional-messaging/about-transact...