Please note that this is available only to the owner and admin users of the account.
To enter your billing details and start your paying Uku account, go to "Settings & Apps" -> Choose your company's app.
Click on 'Choose a plan' to put together a subscription plan suitable to your company.
Depending on your country's billing address you can enter your tax ID.
Confirm the current payment and your subscription plan and you can enter your billing information.