We're sorry to hear you've encountered an issue when attempting to access MySaga.
The following message 'invalid_request: 'client_id' is missing' is typically presented when a VPN is in use.
If you are currently using a VPN, please disable the VPN and close the host program. You will then need to sign out and back into your MySaga account. To sign out, please click your name at top of the page, containing your name. This will expand the menu, revealing the sign out button.
Once these steps have been completed, you should be able to access MySaga without issue.