You have either selected a tax liability account on a transaction where it's not allowed, or haven't specified a tax rate along with it. how can I solve the problem
It's important you're able to enter your transactions without error messages. I'd be able happy to look into this for you.
Normally when you get this error, it means you can’t assign a tax code when using that liability account. Default tax accounts are used to track GST and shouldn't be used in creating transactions in case that's what's happening on your end.
Without knowing where you're seeing that error message, it would be difficult to point you in the right direction but don't worry. Feel free to leave a comment below with more details. You're also more than welcome to contact our customer support team using this link here.