A pleasant day to you, @Nickdobson.
I have some insights to share on why you're getting an message when running a payroll for your client.
When running payroll in QuickBooks Online, you'll need to make sure that you access and create a paycheck on the correct company file. Generating the paychecks from your QuickBooks Online Accountant account can be the reason behind the message that you received.
Once you're in the right account already, you may start the payroll run by following the steps in these links below depending on your subscription:
However, if the problem continues, I recommend contacting our Customer Care Team. They'll be able to check on your clients account and verify the status of the payroll subscription. They can also provide further actions in fixing this issue.
I'm also adding here a help article that you can check out to guide you in utilizing QBO with its great features: Getting started with QuickBooks Online.
Know that you can always visit me here if you have any other concerns. I'll make sure you're all set. Take care!