I'll guide you to the IP address lists you need, Andrei.

You can locate them in the bottom sections of these articles:

• Troubleshoot if customers aren't receiving emails from QuickBooks Online
• Invited user didn't receive your email invitation

I’d also like to share a helpful resource as you set up your dedicated server to interact with the QuickBooks API. We have a dedicated forum called Intuit Developer Community, where developers and users like you share ideas, best practices, and solutions.  If you ever have questions, need insights, or want to explore various approaches related to this topic, it’s a great place to collaborate and find answers to your concerns.

Let us know in the comments below if you have additional questions.