Hi there, @liz-dsigns-com .
QuickBooks integrates with hundreds of third-party software developers, in which it requires their assistance support team. They'll be able to determine whether they can do the integration process or not.
Once verified, to link the CRM app, go to the Apps menu within your QuickBooks Online account.
We don't have any specific programs that we can recommend here. However, I wanted to point you to our App Center. This is where you can find all the third party applications that are sure to work with QuickBooks Online. There are a lot of different options there, so you may find one that works for you.
Check out this page that has all our supported apps: QuickBooks Apps.
Feel free to leave a comment below if you have follow-up questions about integrating a third-party app with QuickBooks Online. I'm always here for you.
