Hi there, Alan.
 
To ensure we can provide you with the best guidance, could you please share more context on when the message or prompt about validation tax code appears? You can share what action you took in QuickBooks Online (QBO) that led to the message. Was it an error or just a tooltip notification?

Any additional information will help us better understand the situation and determine what action is required.

Feel free to share more details with us here. We're here to assist you!