Creating an installed package in Marketing Cloud with Read and Write permissions for data extensions should be used to facilitate the functionality of upserting rows into a data extension using a REST API endpoint. An installed package is a container for one or more API integrations that provides authentication credentials and permissions for accessing Marketing Cloud resources. Read and Write permissions for data extensions allow the API integration to retrieve and modify data in data extensions. References:
https://developer.salesforce.com/docs/marketing/marketing-cloud/guide/create_a_package.htmlhttps://developer.

To use Case data from Service Cloud as part of their current email messaging campaign, Northern Trail Outfitters should use Synchronized Data Extensions on the Case Object witha Boolean filter on the Contact Me field. Synchronized Data Extensions are data extensions that allow marketers to sync data from Sales Cloud or Service Cloud objects into Marketing Cloud using filters and schedules. Using Synchronized Data Extensions on the Case Object with a Boolean filter on the Contact Me field will allow Northern Trail Outfitters to import cases that indicate the customer wants someone to contact them after the case is closed.References:https://help.salesforce.com/s/articleView?id=sf.mc_co_synchronized_data_sources.htm&type