eAuthorize 3.5 runs batch transactions

The eAuthorize plugin is designed to authorize one transaction at a time. You cannot simply call the plugin once and feed it multiple card numbers.
If you are in a position where you must process a batch of transactions, you will have to loop through the unauthorized records and call to the plugin to perform each authorization one at a time.
We must warn you to take extreme care when creating the necessary scripts in FileMaker to perform such a task. Be cautious to ensure that you are handling all possible errors. If there is a bug somewhere in the script, it could be possible that a record in your database doesn’t get flagged properly as having been authorized. Then, at a later time it attempts to authorize again.
If you are utilizing some looping method to authorize your credit cards, the eAuthorize plugin can not be responsible for any duplicate authorizations. If you are getting duplicate authorizations in this manner, check your code very carefully.