Can I create inovice for clinet and purchase order for supplier at the same time?

Hello, userinfo35.

Here to provide you some important information regarding the invoice and purchase order creation process. 

In QuickBooks Online, creating purchase orders and invoices are done separately through an estimate. So, you'll want to record them one at a time. 

You'll want to create an estimate then copy it to a purchase order or make a invoice directly out of it. This will link all transactions involved in the process. Though, you'll still have the option to skip the estimate part and go directly to the invoice or purchase order creation steps. 

To create a quote: 

1. Click the + New icon, then choose Estimate.
2. Choose your client under the Client or Customer drop-down menu. 
3. Enter the important details of the estimate. 
4. Once done, click Save.

You'll be given an option to create an invoice or a purchase order from it. Simply click the button or the drop-down arrow beside the Amount section:

You can find more details about the process here: Copy an estimate to a purchase order.

Need help with your invoices or purchase orders? You can read these articles for a guide:

• Create and send purchase orders in QuickBooks Online
• Create invoices in QuickBooks Online

You're also welcome to read other articles here. They're packed with information that can help you pull up reports, record other transaction forms and manage your lists. 

Do you have other questions? Just post them here or create a new thread. My colleagues and I will be here to assist you with your needs in QuickBooks Online.