Transactions messages are sent to notify customers about recent transactions. For example, messages about the withdrawal of cash, card usage, etc- “Dear customer, your account balance as of 30-APR-19 is Rs 55555 from ABC Bank.” Transactional messages have a 6 character Sender ID and can be delivered 24/7 to any phone number. 

Marketing messages are sent to promote an event, product or for running marketing campaigns- informing the customer about offers, discounts, promo codes, etc. For example. “Now get 4.5% interest on all your fixed deposit from ABC Bank.” Marketing messages can only have numeric Sender IDs, can only be sent between 9am-9pm and cannot be sent to DND (Do Not Disturb) numbers.