If you're having issues accessing a file that has been attached to a task or a project, please try out the troubleshooting steps below:
Make sure you have access to the project where the file is located
If you're not currently added to the project, where the file is located, you can ask someone in that project to invite you to this project.
Log in to your Todoist account in a browser
Attached files open in a browser, even if you're using Todoist in a desktop app.
This means that if you're not logged in to Todoist in your browser, you may not be able to open the file.