I reckon you are trying to launch your trailhead sandbox separately. Try appending /one/one.app to your url after my.salesforce.com - for instance your url will end like this .. my.salesforce.com/one.one.app. Please see that this will lead you to the page where you need to provide your login credentials.
I reckon you are trying to launch your trailhead sandbox separately. Try appending /one/one.app to your url after my.salesforce.com - for instance your url will end like this .. my.salesforce.com/one.one.app.
Please see that this will lead you to the page where you need to provide your login credentials.
If you are not using the below to launch
Please refer the article on how to create userid and password for the trailhead sandboxes so you can login via url ...https://force.desk.com/customer/portal/articles/2659738-how-to-get-a-password-for-my-trailhead-playground?b_id=13478
Hope your query is answered, please mark this as your answer. else please let me know for more queries.