I’ve got you steps to add taxes on your bills in QuickBooks Online (QBO), @mafouad.

You can configure the provincial sales tax as a custom tax in QuickBooks Online (QBO). To include the sales tax when drafting a bill, select the This tax is collected on purchases option.

1. Go to the Taxes menu and click Set up tax.
2. Enter the Tax name, Description, Tax agency name, and Business ID No. 
3. Select the Start of current tax period, Filing frequency, and the Reporting method.
4. Place a checkmark for This tax is collected on purchases option.
5. Enter the rate in the Purchase rate field.
6. Place a checkmark for Purchase tax is reclaimable option if it is reclaimable.
7. Click Save.

Once finished, make a bill and list the cost of the service. Next, select the Provincial Sales Tax rate that you specified in the Tax column.

Keep me posted if you have more concerns about taxes. The Community always has your back. Have a good one!