I'm here to address your issue with QuickBooks Checking.
Beforehand, would you mind adding details to your concern? Can you elaborate more on what you mean about QB Checking being down? This way, I can provide you with an accurate resolution.
When QuickBooks Checking account is down, the invoices will still go through unless the issue is in QuickBooks Online. However, when the problem is in the QB Checking, this will affect invoice payments since Checking this is where all of your customer payments get deposited.
You can check out this resource that contains list of articles that may help you with the most commonly asked Payments questions: QuickBooks Payments FAQ.
Also, I'll be adding these additional resources for more details about using a QB Checking account: