How do i handle purchase order in foreign currency?

Most of the time, i will be purchasing item using foreign currency. when i cleared my payment, it doesnt show in the expenses

First of all, a purchase order is not a financial transaction. See Issue purchase orders | Manager. So you should not expect any impact on your Profit and Loss Statement.

Second, you have not furnished nearly enough information to allow anyone to understand your situation. Describe your currency setups. Explain how you entered the payment. Show Edit screens of relevant transactions.

When you purchase the item its valve added in the Inventry account in balance sheet.

When you purchased a item on credit. A creditor account is opened and shows credit balance.
When you clear the payment- you liability is paid and it will not show any balance.
What is the relation of this with P&L and Manager Accounting Software ?

Sorry for the confusion, only the forex gain/loss is affecting my profit and loss account. as the exchange rate is always changing

Yes, and what is your point?