I am following https://trailhead.salesforce.com/content/learn/projects/get-started-with-salesforce-development/create-a-data-model-using-clicks?trail_id=force_com_dev_beginner and when click on "custom object from spreadsheet" it ask me to login t and after login went to upload page but then immediately it again goes to login page. I have login multiple times but same issue. I am using firefox.
To make this work, I had to create/ reset my lightening experience playground user password. This was necessary due to being automatically signed in to my playground through my Trailhead account.
Use the "Users" list in setup home to force reset your users password - do not do it at the per-user level, since it will prompt for existing password.
Once you have set a password, you can then login using the custom-domain option...
In order to complete the steps in the help article - I needed to be in an incognito window.
