I want to downgrade my plan but I have Multi Currency activated. I have deleted all currencies from GBP (which I use) but QB still says I can't downgrade. Can you help?

I'll share information about downgrading your plan, @cottell.

Multicurrency is available in QuickBooks Online Essentials, Plus, and Advanced. You can downgrade or upgrade to any of these plans.

To learn more about multicurrency, check this article: Set up and use multicurrency in QuickBooks Online.

If you want to continue downgrading your QuickBooks Online plan, visit this article for reference: Upgrade or downgrade your QuickBooks Online subscription.

Also, here's an article that can help you manage your subscription: Manage billing, payment, and subscription info in QuickBooks Online.

Let me know if you have additional questions about managing your subscription in QuickBooks Online. I'm always here to help. Have a great day.

@cottell 

You can't disable the multi currency feature. You should signup for a new QBO Simple Start account and use a migration tool. 

https://get.transactionpro.com/qbo

Otherwise, purchase a 3rd party conversion service.