Thanks @Ami_D I appreciate the response. However, I've heard this story before from @QBCares on Twitter after receiving a private message from them on the matter. I've never heard anything back. I feel there's plenty of information in this thread at this point to resolve the issue. So I'm hoping either engineering can reach out to the community for testing, or if you can keep us updated in the community on the status, that would go a long way in knowing that the issue was at least top of mind.

As I mentioned to @QBCares I'd be more than happy to provide any necessary information from our side, and test if needed. Additionally, if these 3 IP addresses are valid IPs for QuickBooks invoicing, they really need to update the KB article referenced throughout this thread and in my original post. While it shouldn't be necessary that we add IP addresses to an allow list, I want it documented properly if that's the route we must go. This is obviously not a solution to most as you've seen however.