Can we link Purchase Invoice to Sales Invoice?

Hello there, @ravindrakumar-ar.

Just to make sure I got it correctly, would you like to link the Purchase Order (PO) to your customer's invoice? If so,  you can link these transactions by utilizing the Billable expense feature from the settings. The steps below will walk you through completing the tasks.
 

Create a PO:

1. Go to the +New button.
2. Select Purchase Order under the Suppliers column.
3. Enter all the important details. In the line item, add the customer you want to link with the PO. Click the Customer field to choose the appropriate one.
4. Click Save.
   

Once done, create an expense or bill.

1. Turn on Billable expense. 
2. From the +New button, select Expense.
3. Select the name of the payee under the Payee field. The PO you created earlier will show up from the right side. Click Add.
4. Make sure to tick the Billable box. Then, add the customer name.
5. Click Save.
   

Create an invoice and add the expense you created. Under the Customer field, make sure to select the correct customer's name to populate the billable expense you created. You can take a look at the sample screenshot below.

I've gathered some articles about receiving payments and customising sales forms in QBO:

• Record invoice payments in QuickBooks Online.
• Customise invoices, estimates, and sales receipts.

If you have more questions about handling transactions in QuickBooks, please don't hesitate to add another post below. I'm right here to help. Take care and have a good one, ravindrakumar-ar.