Hey there devam,
Welcome to the QuickBooks Community! Thanks for reaching out to us here. Having the correct sales tax calculation is important. I would be happy to point you in the right direction.
Here is a helpful guide to ensure Sales tax is correctly set up in your account. in addition, I'd like to make sure you get the support you need. Since you're using QuickBooks Self-employed, I recommend reaching out to their support team. They'll be able to better assist you. You can reach them by following this link.
I hope this helps!