Explanation
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.