Merchant ID (MID)
DEFINITION
A merchant ID (MID) is a unique identifier that a payment processor, acquiring bank, or card network assigns to a business so transactions can be routed to and settled with the correct merchant account.
RELATED TERMS
A merchant ID, or MID, is a unique identifier that a payment processor, acquiring bank, or card network assigns to a business so that transactions can be routed to and settled with the correct merchant account.
A merchant ID is not a Recurly construct. It is issued outside of Recurly by whichever gateway, processor, or acquiring bank a business works with, and it tells the payment networks where a given transaction belongs. A single business can hold more than one MID at the same time. It is common to keep separate MIDs for different use cases, such as production and test environments, or for different production uses such as card present and ecommerce. Some card networks, such as American Express, may require their own dedicated MID that is distinct from the one used for other card types. When a business changes payment gateways or adds a new one, its MIDs typically change too, since each gateway relationship usually comes with its own merchant account setup.
Why it matters
The MID is the piece of information that support teams, gateways, and card networks use to identify and troubleshoot a specific merchant account. If a MID is missing, mismatched, or not carried over correctly during a gateway migration, transactions tied to that MID can fail or decline, because the card network cannot connect the transaction to a valid merchant account. Subscription billing depends on repeat, unattended transactions over time, so keeping MIDs correctly configured across every gateway a business uses is part of maintaining healthy authorization rates.
With Recurly, MIDs are configured at the gateway level as part of connecting a gateway to a Recurly site, and Recurly integrates with a wide range of payment gateways. Recurly also supports gateway routing and network transaction ID handling that can help protect authorization rates when a business is using more than one MID or moving between gateways.
How to use
Confirm the MID assigned to the business by each payment gateway or processor before going live, including any sandbox and production MIDs.
Check whether any card networks used by the business, such as American Express, require a separate dedicated MID.
When migrating to a new gateway or adding one, verify that all relevant MIDs are set up and mapped correctly before the migration goes live. Pay special attention to American Express, which has a unique SE MID mapping capability.
Have the MID on hand when opening a support case with a gateway or processor, since it is typically required to identify the merchant account.
After a gateway or business change, consider reverifying stored billing information so that the card issuer associates future recurring transactions with the new MID.
Benefits and examples
Keeping MIDs organized pays off in a few concrete ways. Support teams for gateways and processors usually ask for the MID first, so having it ready speeds up escalations. Confirming MIDs are set up correctly for every card type before a gateway migration helps prevent a spike in declines afterward. And keeping sandbox and production MIDs separate stops test transactions from hitting a live merchant account, or the reverse.
For example, a business running its Recurly billing through a Fiserv Commerce Hub integration needs to add its Merchant IDs, one for sandbox and one for production, inside the Commerce Hub Developer Studio, with separate API keys generated for each MID.
Frequently asked questions
Does Recurly assign my merchant ID? No. A merchant ID is issued by the payment gateway, processor, or acquiring bank a business works with, not by Recurly. Recurly stores and uses the MID information tied to the gateway configuration on a business's site.
Can a business have more than one merchant ID? Yes. It is common to have separate MIDs for sandbox and production environments, and some card networks may require a distinct MID from the one used for other card types.
What happens if a merchant ID is not carried over during a gateway migration? Transactions tied to a MID that was not properly migrated or reconfigured can decline, because the card network cannot match the transaction to a valid merchant account. This is a common cause of a decline spike right after a gateway switch.
Why would American Express need a different merchant ID than other card types? Some gateways route American Express transactions differently than other card networks and may require a separate, dedicated MID for American Express specifically. If that separate MID is not configured correctly during a gateway change, American Express transactions can be declined even when other card types are unaffected.
Is a merchant ID the same as a merchant account? The MID is the identifier tied to a specific merchant account with a processor or acquiring bank.
