When I try to upload a .txt file to my shopware installation I only get an error saying this format is not supported.
I have a .txt verfication file for a 3rd party system that I need to upload to the system.
How can i, through the gui, add a .txt file to my shopware installation?
I assume you want to do a verification for a service like google, right?
In that case, you have to upload the file to your installation, which can't be done via the Shopware Backend.
You have to use a ftp client like filezilla or winscp (both very simple).
Your hoster should provide you with the needed login data (server, name, password)
From here, you just have to navigate to the part of the installation, where you want to upload the file to and, well, just upload it.
I hope I could help you.