I have sterling purchase invoice and paid in usd, can you please guide how to pass that entry please?

I can guide you with recording your payment in USD, @rosary-wheeler-i.

First, you must turn on the multicurrency feature in QuickBooks Online (QBO). It'll help you record foreign transactions without worrying about exchange rate conversions. Refer to this article for more information on how to add, delete, and add an account that uses a foreign currency: Turn on and use multicurrency in QuickBooks Online.

Then, create a customer in USD currency. Follow the steps below:

1. Go to Customers & leads and select Customers.
2. Click on New customer.
3. In the Customer Information window, provide all the needed information.
4. Click the Payment and billing.
5. In This customer pays me with field, select USD as the customer's currency. 
6. Select Save.

Refer to this article on how to create a customer in a foreign currency: Assign a foreign currency to a customer in QuickBooks Online.

Use that customer in USD when recording the bill . When recording the payment, use exchange rates from IHS Markit or your own exchange rates for foreign currency transactions. See this article for detailed guidance: Enter and use your own exchange rates. 

From here, you can run either the Customer Balance Detail report or the Supplier Balance Detail report to view unrealised gains or losses on those reports. Refer to this article for more information about generating this report: Frequently Asked Questions about Home Currency Adjustments.

I'm always here if you need further help in recording your payment. Let me know in the Reply section below. Have a great rest of the day!