This error usually appears where AMKA entry is required (e.g. sports matches).
Please check that your AMKA has not been entered again for purchase for the same match or in case of an unsuccessful attempt you will be able to repeat the process again in approximately 20 minutes.
For further information you can contact us via email at email@example.com or via Live Chat.
P.S. : The AMKA entry is available only for Greek sports matches.