I had a problem a while back where my receipts weren’t getting through because they were being treated as spam by gmail (receipts@quickfile is, or at least was at the time, a gmail mailbox, and if the gmail tools treat your domain as spam then QuickFile doesn’t see the message). You can check whether this is the case by sending the same email to a gmail address of your own and see if it gets sent to spam.
An alternative might be to try the Dropbox integration, or my connector for Google Drive, to import receipts from there. I have the google drive connector set up and then in the gmail app I can just save attachments direct to the drive folder that then syncs to QuickFile.