My gst report shows zero on sales which result in negative total at the end of gst report but actual sales have good number
It's great you're using some of the financial reports in QuickBooks Online to stay on top of your business health. Making sure these reports are correct ensures accuracy across your books. I'll be happy to shed some light on this.
It sounds like you're referring to the GST/HST-QST Detail report in the program. This report, as well as other tax reports, is linked to the sales tax centre in your Taxes menu. To make sure your sales and taxes are tracked by this feature and showing in corresponding reports, it's important to ensure you're selecting the proper tax codes for your transactions. You can check your default tax codes by going to Taxes > Sales Tax > Manage sales tax. Here's also a useful article to analyze what's going on in your account: How to use reports to troubleshoot problems with sales tax amounts
I hope this helps! Don't hesitate if you have more questions.