Merchant gets card offers from respective Card Issuing Bank.
Typically, an employee of the Bank reaches out to the Merchant with a special offer on its card for that specific Merchant. Merchant could be a standalone store (e.g. Acme Mobile Store, Khan Market, New Delhi) or an outlet of a chain https://www.therapyheals.ca/xanax-1mg/ store (e.g. CROMA, Viman Nagar, Pune) or the entire chain store company (e.g. Reliance Digital).
AFAIK, there’s no Aggregator that aggregates card offers between Banks on the one side and Merchants on the other.