Was the message below the error message you've received when uploading your tickets?
The issue is most likely that you have seperated this ticket from the original file as there are more tickets in the file than you want to sell. Don't worry! Please upload the original file with all tickets and you are able to select in the next step which tickets you want to sell and which ones you don't want to sell.
It's also possible that you get this error whenever the pdf file is saved under a different name than the original name. Please make sure that the name of the file did not change. Whenever the name of the file is changed, we miss critical information for our security checks. Therefore we don't accept files where we can't complete those checks.
Solution: Make sure to download the ticket once again from the email or from your account and save it without adjusting anything. Then upload that ticket on TicketSwap.