In order for a business to start processing online payments, it must go through a merchant onboarding and merchant underwriting processes. In the process of merchant onboarding merchant applicant submits the required data to the underwriter. The underwriter reviews the data and grants MID to the merchant. Merchant data is input into the payment gateway and the merchant can start processing. When all or some of these processes are performed manually, the whole procedure can take as long as several days. Automation and streamlining of merchant onboarding and underwriting processes sometimes allows the merchant to start processing right after merchant application submission. One of the commonly used approaches is allocation of pre-assigned blocks of MIDs, which payment aggregators can distribute among merchants with specific MCC codes. Another approach is API- or file-based process for merchant data submission.
More information on streamlining of merchant onboarding process is available in the respective article on on Paylosophy.