Electronic Commerce Indicator (ECI) is a value returned by Directory Servers (namely Visa, MasterCard, JCB, and American Express) indicating the outcome of authentication attempted on transactions enforced by 3DS.

Possible value returned by Visa, American Express, and JCB and its interpretation:

• ECI 05: 3DS authentication was successful; transactions are secured by 3DS.
• ECI 06: authentication was attempted but was not or could not be completed; possible reasons being either the card or its Issuing Bank has yet to participate in 3DS.
• ECI 07: 3DS authentication is either failed or could not be attempted; possible reasons being both card and Issuing Bank are not secured by 3DS, technical errors, or improper configuration.
  

Possible value returned by MasterCard and its interpretation:

• ECI 02: 3DS authentication is successful; both card and Issuing Bank are secured by 3DS.
• ECI 01: 3DS authentication was attempted but was not or could not be completed; possible reasons being either the card or its Issuing Bank has yet to participate in 3DS, or cardholder ran out of time to authorize.
• ECI 00: 3DS authentication is either failed or could not be attempted; possible reasons being both card and Issuing Bank are not secured by 3DS, technical errors, or improper configuration.