Okay, I am going to clean up the mess created by users who obviously either don’t understand Manager or don’t understand the application of the GST / VAT taxes.
Firstly @Mark, the reason you ended up with the P&L (160 sales & 160 COS) as you did was because you processed the refund transactions incorrectly. If you had followed the Manager’s Guide on Refunds (Pay a refund | Manager) you would have ended up with a zero P&L as per @Hennie.
Secondly, @patch your various bloated commentaries are absolute garbage on two grounds, firstly it is obvious you haven’t read any GST/VAT Tax Acts and secondly your understanding of Manager is obviously very limited.
The Tax Acts first, if we use the Australian Act (A New Tax System (Goods and Services Tax) Act 1999) you will have the following exact quotations:
Note how the act refers to “taxable supplies” not sales and “input tax credits” not purchases. That is how I knew your repetitive references to sales and purchases in your commentary was garbage, that is, it wasn’t Tax Act based.
Now to further expand upon the notion of taxable supply (not sales):
Why the term supplies instead of sales, because supplies includes Balance Sheet transactions (asset purchases) whereas sales by terminology is limiting to P&L. To illustrate in accordance with the Act; the seller is suppling and the purchaser is being supplied regardless of the accounting outcome, be it a BS or P&L transaction.
Now for input tax credits, note again how there is no references to “purchases”
The above citations are generally equal across all GST / VAT Acts, especially as the Australian GST Act is broadly based upon the European VAT Acts, which came first.
@patch this is the type of Tax Act substantiation that you failed to deliver to support your false and malicious allegations against Manager’s handling and reporting of taxation.
Furthermore @Patch if you as a User had understood and applied the applicable Manager’s Guide for Refund Transactions to your phone example then you wouldn’t have resorted to your repetitive claims that Manager had corrupt taxation reporting
In addition, you have repetitively accused Manager within post #15 with the following allegation “When a Manager user enters a Receipt or Payment with a tax code that means they are not using Manager to generate the substantiation documentation required in most jurisdiction. By which I mean the Manager user is not using Manager to generate the tax invoice.”
This once again informs the forum of your naivety and ignorance of the features within the programme. If you had bothered to review the Receipts and Payments form you will have noted the option 
, this enables the user to rename the Cash Receipt to be anything, such as Tax Receipt or Tax Invoice or any other title required as substantiation documentation by the jurisdiction.
In closing, Manager isn’t responsible for users who can’t use the programme in accordance with the Guides and furthermore Users shouldn’t abuse and make defamatory comments about the programme because of the their incompetence to follow the Guides.