Glad you visited the QuickBooks Support forum, Nicola.
I want to make sure you're able to get the answers you need with migrating your data. For this, we need to forward you over to our partner support.
We have a separate forum called Intuit Developers, where you can find engineers who can help with API concerns. Click this community link, and post your question there: Intuit Developers Community.
Visit our support page again if you have other concerns related to QuickBooks. I'm also here if you need further assistance. Have a great rest of the day!