I set up the GST for 8% but the tax return only captures the invoice value but not the GST calculation. How can I rectify this? The rate is correctly set as 8%.

Thanks for visiting us here, userbmongia. Allow me to share information and ensure your GST returns get resolved.

Since you've mentioned tax returns only capture the invoice value, and you've already set up the GST of 8%, you'll want to consider reviewing your transaction and make sure that the GST tax of 8% was added to the invoice. To do that:

1. Sign in to your company file.
2. Go to the Sales menu and select the Invoices tab.
3. Find and open the invoice transaction.
4. Review all necessary details and ensure the GST tax of 8% is added.
5. Once done, select Save and Close.

Additionally, you can also run the GST Liability report to check how much sales tax you owe and why you owe them. 

Moreover, I'm adding this article to guide you in filing and recording your GST tax payments: File your GST return and record tax payments in QuickBooks Online.

Let us know in the comments below if you require additional assistance reviewing and managing your sales taxes.