Hi there Pranav,
Thanks so much for your reply, it's great to hear from you :)
Regarding your question, our transactional API is actual exempt from the "message limits" setting that we provide for campaigns and newsletters. The reason for this is because the use-case of transactional messaging is generally that a message needs to be sent in response to an action or request from the customer. By that nature, we wouldn't want to impede on those messages being delivered. For reference, we do mention this in our documentation here: https://customer.io/docs/message-limits/
So if there are perhaps instances where a message is transactional but is one that you'd like to limit, the options here would either be to include some logic in your app where the transactional API requests originate from... or potentially switching to an event triggered campaign that can be limited via message limits.
I hope that helps to provide clarity for you here, Pranav! If you do have any further questions or need anything else going forward, please don't hesitate to let us know.
Best,
Elena