Introduction about payment integration Collecting the sales you worked so hard to generate should be simple and seamless. Our platform is fully integrated to enable invoicing, billing, collection, and related communications all in one place. MerchantStronghold ™ facilitates online purchases from a merchant’s website and helps them to collect payment from the end customers through E-Check, Credit and Debit Cards etc. It is an intermediary that assembles the online payment options offered by various banks, And cash card brands onto a single platform with minimum technical integration with merchant website.