We have 1 customer and they are the suppliier .they are paying the sales cash after deducting the purchase ..how can i do this entry?

Thank you for visiting the QuickBooks Community, balady-baladyfoo. Let me share some insights on handling transactions when you have a customer who is also your supplier. I'll also make sure you can easily record the entry in QuickBooks.

When a customer is also your supplier and you have both entries, you can record a barter transaction in QuickBooks Online. This occurs when you and your customer exchange goods and services. To enter the entry, you’d enter an invoice and a bill to record the products or services you’re exchanging. 

Beforehand, I suggest you add your barter partner as a supplier (for the bill) and customer (for the invoice). Since you can’t have the same name in both lists, make one of the names slightly different to avoid duplicates. 

To start with, you have to set up the barter bank account in QBO. 

Here's how:

1. Click the Gear icon ⚙ and select Chart of accounts.
2. Click the New button to create a new account.
3. Under the Account Type dropdown, select Bank.
4. Under the Detail Type dropdown list, choose Cash on hand.
5. Enter the account name. (ex. Barter Bank Account)
6. Click Save and Close.

In your case, it seems that the sales are bigger than your purchase amount. Thus, it can cause inequality in the value and having a balance due on the invoice. To clear it out, you have to record an invoice payment to the received cash. To do so, you can follow the steps below:

1. Click the + New and choose Receive payment.
2. From the Customer dropdown, select your supplier’s (barter partner) name. Note: The details and info from the invoice you’ve created earlier will appear under Outstanding Transactions.
3. Fill in the date and amount you received.
4. Enter the other nessasary field.
5. Click Save and close.

After that, you may open this article to see the further steps to perform the complete process: Record a barter transaction.

Lastly, you can click this article if you need steps to run different reports in QBO to see a snapshot of your business: Run reports in QuickBooks Online.

Please let me know if there's anything else I can assist with recording transactions in QuickBooks. I'm always ready to lend a hand, balady-baladyfoo. Have a wonderful day!