Are you referring to the concern that HST is not being added to the total amount of the invoice or the balance due? If that is the case, you'll have to verify if you've selected the Inclusive of Tax option. This ensures that taxes are calculated and included on your invoice. I'm here to guide you on how to deal with your tax concerns, Miriam.
It's also possible that you may have selected the Out of Scope option, which will result in the sales tax not being automatically calculated or added to the Total amount. You'll have to make sure to select the Inclusive of Tax setting and choose the appropriate tax rate to ensure that the tax is properly computed and included in your invoice.

On the other hand, regardless of whether taxes are applied to your invoice or not, the total amount will still show the same total amount since these taxes are already deducted from the invoice total amount. I've added a screenshot that shows the same total amount of the invoice with or without taxes:


However, if you're unable to locate HST after you added it in QuickBooks, you can refresh the page.
For more information on how to manage sales, check out this article for more details: Set Up and Use Sales Tax in QuickBooks Online.
Additionally, QuickBooks Online (QBO) offers a variety of reports so you can easily track taxes. I've added this handy resource for your guide: Run Reports in QuickBooks Online.
Keep in touch if you have any other queries or concerns about taxes or if you're referring to something else. I'm always here to assist you further.