To avoid data loss and ensure reliable data transfer to Marketing Cloud data extensions, follow these best practices:

Handle 'Not Authorized' Errors: If a 'Not Authorized' error occurs, it is likely due to an expired or invalid access token. Request a new access token and retry the API call.

Retry on Server Errors: If a server error occurs, it might be a temporary issue. Ensure the server is available and retry the call.

Token Expiry Management: Store the expiry time of the access token and request a new one before the old token expires to prevent authorization issues.