It is recommended, but not necessary to upload campaign data once per day. You should do this around the same time, in order to get accurate daily statistic reports. You can only upload one campaign file per day. This should be the campaign file that you have downloaded before from your Amazon Advertising dashboard.
When you are at the Upload menu section you will see the current date at the top. This date reflects the server date and may not be identical with your local time zone. To check the time zone of the server please have a look at your user status, which you will find under the User menu section.
If you try to upload the same or any other file again the program will first check the database if there are data already uploaded for the current date. Please keep in mind that the Amazon campaign file you download does not contain a date stamp. This date stamp is provided when your campaign file is uploaded into your account database.
You will see this message when you try to upload your campaign file a second time for today. Keep in mind that your date may already be changed but not the server date. Simply check under the user account menu what date you will see there.