XID
What is an XID?
An XID is a unique transaction identifier used in the authentication process. It acts as a reference key that ties a single 3DS authentication to the payment it belongs to, so the authentication result can later be matched to the right transaction.
3DS adds a layer of security to online card payments by authenticating the during checkout. The XID is the value that links that authentication exchange to the underlying purchase.
Key facts
- Unique to a single 3DS authentication attempt
- Generated as part of the 3D Secure protocol, not the general payment authorization
- Links authentication data exchanged between the cardholder's bank, the merchant, and the card network
- Used to track and reconcile 3DS transactions
- Helps associate an authentication response with its corresponding payment
How it works
During a 3DS-authenticated payment, the XID is passed between the parties in the authentication flow: the cardholder's , the merchant, and the . It travels with the authentication messages so each response can be tied back to the specific transaction that triggered it.
Because the XID is standardized across payment platforms and networks, it gives everyone in the flow a common reference for reconciling 3DS activity, which supports tracking authentication outcomes and reducing the risk of unauthorized card use.
XID vs transaction ID
The XID is sometimes described as a transaction identifier, but it isn't the same as a general payment transaction ID.
| Attribute | XID | Transaction ID |
| Scope | The 3D Secure authentication exchange | The overall payment transaction |
| Generated by | The 3DS authentication flow | The processor or gateway handling the payment |
| Main use | Reconciling authentication data to a payment | Tracking and referencing the payment itself |
Why it matters
The XID gives the parties in a 3DS flow a shared key for matching an authentication result to the exact payment it authorized. That link is what lets a merchant or bank confirm a transaction was authenticated when reconciling records or reviewing a disputed payment, so authentication evidence stays attached to the right purchase instead of being lost between systems.
