Not able to connect sandbox to the hubspot developer account trial.
Getting 'This app hasn’t been granted all required scopes to make this call. Read more about required scopes here: Working with OAuth - HubSpot docs.
Hey, @PTrivedi8 
Can you clarify your goal, please? I ask because Sandbox accounts are an Enterprise-only subscription feature and are not added via an API call.
Please note: a standard sandbox account is different from an app developer account, which is used for developing HubSpot apps and integrations.
If you are attempting to do something else, please update your post with those details and the community will try to help.
Best,
Jaycee