I thank you for sharing the troubleshooting steps you've performed, @JulioDE.
Let me share additional information so you'd be able to connect your Monzo account with QuickBooks.
The error message indicates the DNS server is unable to find the IP address connected with the domain. To move past the issue, you’ll have to configure the network setup. Also, using the new Open Banking connection in QuickBooks, you may have pop-up blockers on your browser that are active. This prevents you from completing the setup and proceeding to the transaction page. You'd want to disable the pop-up blockers on your browser and try to connect again. Alternatively, refresh the page to allow for the consent page to fully load.
On the other hand, you can try accessing your QuickBooks Self-Employed account using a regular browser from a Windows PC or an Android device. Lastly, I'd recommend reaching out to your IT personnel for assistance with the process.
If the error persists, I would recommend contacting our support. That way, they can start a screen-sharing session to see your setup. They might take screenshots for documentation and further checking.
Alternatively, you can upload your transactions using Web Connect files.
For your next step, you can check out the article about assigning, categorising, editing, and adding downloaded or uploaded bank transactions.
If you have other questions in mind, please don't hesitate to go back to this thread.