Hi @Sakofri 

I assume you are not in cloud. I have a step by step instruction for offset. Please see below

Hope this helps

Purpose: The purpose of this lesson is to show you how to make offsets between customer debit and credit invoices/installments as well as between payments on account and invoices/installments. Parked payments can also be offset. The offset function does not cause any cash flow, and the total amount must always be zero (0).

Manual Customer Offset

Purpose: The purpose of this exercise is to show you how to offset a customer debit invoide to a payment on account. It requires that you have created a debit customer invoice not paid and a payment on account that has been paid. Also credit invoices can be offset to a debit invoice (not paid).

1. Open the Customer Offset window.
2. Click the General tab, and create a new record.
3. Enter the payment currency, i.e., the currency of all items included in the offset.
4. Click the Transaction tab, and create a new record. Enter Series ID CUPOA(Customer Payment on Account) in the Series ID field and press the List of Values in the Inv/Prepaym No field. Mark the payment on account line and press OK.
5. Enter a new line and enter the debit invoice no or use the List of Values in the Inv/Prepaym No field.
6. Save your changes. Right click in the header and press Approve. A window appears with the payment information.
7. Click OK to close the window.

Note: Instead of entering the lines manually, you can right-click and then click Select Batch to open a window that you can populate with all open ledger items.

1. Enter the information in tab General and save.
2. Go to the Transactions tab and take right mouse button, press Select Batch.
3. Highlight the two items that should be offset, and click OK. These items are automatically copied to the Customer Offset window.

8. Right click in the header and press Approve. A window appears with the payment information.
9. Click OK to close the window.