I have a couple of solutions to help you resolve the error, matthew-humphrey.

Let's try changing the data connection on your device:

• If connected to Wifi, turn it off and use cellular data.
• If connected to cellular data, connect to Wifi.

Once done, restart your QuickBooks app and try to signing in to your account.

If you're still getting the same error message, you'll want to clear the app's data.

• Android: From More Options ⋮, tap Settings, then select Refresh Data, and then tap Yes.
• iOS: From the Menu ☰, select Help & Feedback, tap Refresh Data, and then select Refresh.

Otherwise, uninstall and reinstall the app. I've got this article for the troubleshooting reference: Troubleshooting Quick-Start Guide for the QuickBooks Online app.

You can always get back to me if you have other questions or concerns. I'd be glad to help you out again. Take care!