Is it the right Google account?
If you go to https://drive.google.com, verify you are logged into the account you would like to share files from. If not, switch to the account that has the Google Drive file.
Afterwards, refresh the Eduflow submission activity page and try again.
Browser cookies and security settings
Are you allowing cookies from the Eduflow site and Google Drive?
Browsers are getting more strict when data is exchanged across websites, meaning you may need to ensure you've permitted both Eduflow and Google Drive to talk to each other.
Check your browser settings to see if you are blocking cross-site tracking, third party cookies, or haven't authorized app.eduflow.com - or whichever domain Eduflow is hosted on - to your cookie whitelist.
If you've encountered the error "The feature you requested is currently unavailable. Please try again later.", this may apply to you.
To allow cookies, you can try this guide: https://help.eduflow.com/en/articles/4598908-how-to-allow-cookies
Afterwards, refresh the submission activity page before trying again.
Could browser extensions be interfering?
Some browser extensions, notably ad blockers like AdBlock and uBlock, are known to block Google Drive.
If you try disabling browser extensions you have running in the browser, you can refresh the submission activity page, and try again. If it works then, the extension may be the cause.
Google Drive sharing permissions
Sometimes files aren't allowed to be shared due to file settings. To check if a Google Drive file has had sharing restricted, open "Sharing" for the file an click the cog:
If "Viewers and commenters can see the option to download, print, and copy" is unchecked, assure it's checked:
Afterwards, refresh the submission activity page and try to attach the file again.
Troubleshooting tips
When trying any of the solutions on this page, always refresh the submission activity page after.
Try a different machine, if one is available.
If you're using Safari, especially on iOS:
Relax cross-site tracking rules in Safari's settings
If available, try a notebook or PC with Google Chrome
Run through General troubleshooting.
These can be extremely effective, since browser cache and settings are the leading cause of Drive attachment issues.
Still need a hand?
Contact support and let them know the Activity URL you are having an issue with and what you've tried so far.