We have some supported third party apps that can automatically sync data between FreshBooks and QuickBooks Online (QBO), such as FreshBooks by OneSaas. You can check these apps by clicking Apps in the left navigation bar of QBO.
If the available apps are not suitable for you, it's best to reach out FreshBooks. They'll be able to provide you the proper steps if there are other ways of transferring your details from the app to QBO.
Feel free to
keep me posted if you have other questions about connecting third party apps