I'm here to help guide you to the right support who can help you with importing the transactions from Microsoft Dynamics Great Plains to QuickBooks Enterprise.
To help you further with mapping the fields of your customer's data, I suggest contacting/getting in touch with our Intuit Developer Team. They have the chance to access you and check your account securely and help you with the process.
You may use this link to get in touch with the Developer Team: https://developer.intuit.com/app/developer/homepage.
To learn more about converting data from Microsoft Great Plains to QuickBooks Desktop Entreprise, you can check it here: Data Conversion Details for Microsoft Great Plains.
Please know that I'll be right here to help you if you have any other QuickBooks questions, just add a post/comment below. Have a good day ahead!