Transactions can have only one foreign currency at a time.

You can only use or assign one currency per transaction, account, customer, vendor/supplier at a time. You might need to create another vendor/supplier  to assign that foreign currency to.  

Here's an article about Multicurrency: https://quickbooks.intuit.com/learn-support/en-sg/banking/about-multicurrency/01/381735

The screen looks like that, does everything correct?

the supplier is in USD and both categories and products are in USD. What else shall I do?

Hi there, @HEMIN.

Yes, you're on the right track when assigning currency to your supplier.

The Multicurrency feature in QuickBooks Online helps you save transactions in foreign currencies. Knowing how multicurrency works in the system is essential to record your transactions. I'll be happy to share more on this.

The currency assigned to your Products and Services is your home currency and no foreign currencies can be displayed. This is because your inventory items are linked to Income and Expense accounts which always use your home currency in the system. 

However, you can set up suppliers and customers in a foreign currency of your choice. This way, if you create a bill towards a USD supplier with your home currency being CAD. QuickBooks Online will display the total cost of the bill in both USD and CAD. To learn how to assign multicurrency to suppliers and customers, check out these articles.

• Assign a foreign currency to a customer in QuickBooks Online
• Add a supplier with a foreign currency in QuickBooks Online

If your transaction doesn't show both currencies despite everything being set-up, it could be due to a browser issue. Temporary internet files that accumulate in your browser can sometimes cause bugs in the software. To ensure your app or browser is running the program as designed, I recommend following the troubleshooting steps in this article: Clear cache and cookies to fix issues when using QuickBooks Online.

If you have more questions, reply below. Have a good one!

Hi   SolarRed

Thanks for your support. I tried but didn't help 

Hi MaryAnn_E

Thanks for the explanation.

In QB I set USD as a home currency, when I create a new customer I also choose USD , then when I make an inovice it gives me the error. But when I choose IQD no error appears, however, all my products are intered in USD, so the calculation all becomes wrong actually when I choose IQD. 

I have followed the steps in this articel Clear cache and cookies to fix issues when using QuickBooks Online.. 

if possible to solve it for me remotely using team viewer or any other application would be great.

Many thanks

Let's find out why you're getting an incorrect calculation, HEMIN.

What specific error are you getting when trying to create an invoice?

You'll want to make sure that you've correctly set up the US currency as your home currency and that you haven't activated the Multicurrency feature so it will correctly calculate your invoice. 

However, if the set up is correct and you're still getting an error, I recommend contacting our phone support team to help you double-check your transactions. Yes, we do have a team viewer that can help you remotely work to correct your account. They will also be able to view it in a secure environment.

Here's how to reach them:

1. Sign in to your QuickBooks Online company.
2. Select Help (?) at the top right.
3. Enter your concern, then select Let's talk.
4. Select Contact Us to connect with a live support agent.
5. Choose a way to connect with us:
   • Start a chat with a support expert.
   • Get a callback from the next available expert.
   • Ask the community to get help from businesses like yours.

You'll want to browse these help articles to guide you if you have questions about QuickBooks Online.

Keep me posted if there's anything else you need about entering transactions. I'll always be right here to help you.