Hi there, alice-toh-zb.
If you're on a trial version of QuickBooks Online, then you can subscribe to the plan by updating your billing information.
I've got this article for reference: Update the payment information for your subscription.
If you have QuickBooks Desktop in the U.S version and want to register the program, you can check out this article for additional details: Register QuickBooks Desktop using Intuit Account.
When prompted for the validation code, I'd recommend contacting our Customer Care Team by following these steps:
Please know that we are always around to help you if you need anything else. Thanks.
How do I create a QuickBooks account?
Create, edit, or delete account in QuickBooks Desktop
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