Have you filed yet? or are you trying to print before filing?
You will need to pay before you print your 2018 tax forms or tax return. Please see this TurboTax FAQ:
https://ttlc.intuit.com/replies/3338601
For more information on printing your return and step-by-step instructions, please see the TurboTax FAQ below and click on the version you are using.
https://ttlc.intuit.com/replies/3301671