Thanks for letting me know that you've tried one of our recommended troubleshooting for the desktop app, ABK1.

What we can do now is check if your computer is compatible to use the QuickBooks app. For the system requirements, please check out this article: QuickBooks App for Windows and Mac: General support.

If you're still getting the error, please consider giving us a call. Log in to your QuickBooks account through a web browser and follow the steps below. This way, we can investigate this further why it is happening. 

1. Click the Help icon at the upper right corner and select the Contact us button below.
2. Enter a brief description of your concern. Let's say for example " 504 Gateway Time-out ".
3. Click Let's talk to process your concern.
4. You can either choose to Get a callback or Get the number to talk to one of our specialists.
5. Enter the needed information and click Confirm my call.

I'll be around in case you have other about QuickBooks. Take care!