Backups And Demos
When you start connecting to your own Solution to Quickbooks Online we highly recommend that you work with a backup of your solution first. We also recommend that you use a different demo only QuickBooks Online account. If you do that you will not have to worry about errors screwing up the data in either your FileMaker solution and/or Quickbooks Online.
Switching to Live
If you are using the starter solution ( ie fmQBO2.fmp12), then that's where most of the code changes will be. Thats makes it easy to just drop in your live copy when you ready to go. Even if you aren't using the Starter solution, placing all the sync code in a separate fill is a good idea, for this and other reasons.
Demo QuickBooks Online Accounts
The simplest thing to do is to just get another account temporarily. You can usually get one for 30 days for free. You can have as many accounts as you like. They all be accessible to you through fmQBO. You can even switch which accounts has a license.
If you already have a regular Account, you can sign up at http://developer.inuit.com and get a Sandbox Account. These are free, but they have data in them. fmQBO does allow you to Connect to Sandbox account, but you'll need to have signed up with a regular account first.
More information on Sandbox accounts can be found here.
You will need to login first.