I'd be glad to assist you in adding a customer discount and reducing the sales tax on your customer's sales form, Jean. I'll lay down the steps below.
 

In QuickBooks Online (QBO), the method for setting up and applying discounts differs based on whether you're using the new or old invoice experience. The system automatically generates a "Discounts given" account in your Chart of Accounts to track these adjustments. Before you start using reductions, you'll need to enable this feature in your settings.
 

If you're using an old layout, here's how to activate and add this on an invoice:

1. Go to Settings and click Account and Settings.
2. Select Sales.
3. In the Sales Form Content section, hit the pencil icon.
   
   
   
   
4. Switch on the Discount setting.
5. Click Save, then Done. 
    

Then, refer to the steps below to apply the discount as a percentage or a flat amount:

1. Select +New and choose Invoice.
2. Fill out the form and add your products and services in the designated column.
3. Choose Discount percent to enter discount as a percentage or select Discount value to enter as a specific amount.
   
   
   
   
4. Enter the percentage or amount in the discount field.
5. Hit Save and Close. 

Alternatively, you may add them as a line item on your sales form where you include a description of what this is for.

However, if you're on a new layout:

1. Go to +New and choose Invoice.
2. Click ⚙ Manage. 
3. Select Payment options.
4. Turn on the Discount setting to add a dedicated field.
5. Fill in the necessary information.
6. Pick between a flat discount or a percentage discount and hit Save. 
    

For further details, visit this resource: Add a discount to an invoice or sales receipt in QuickBooks Online.

Regarding reducing sales tax, you have the option to manually create a custom rate. However, please know it should be recommended by the State Agency to record the accurate sales tax. 

Here's how to generate a personalized rate:
 

1. Go to Taxes or Click GST in the left panel.
   
   
   
   
2. Select the Edit GST dropdown and choose Edit rates.
3. Click the Add Tax Rate button.
   
   
   
   
4. Enter the required fields. 
5. Under Tax Agency, tick Sales.
   
   
   
   
6. Add a sales rate percentage and complete the other details.
7. Hit Save.

Additionally, I'll provide you with a helpful resource for generating transaction records for customers who make on-the-spot payments for goods or services at the time of sale: Create sales receipts in QuickBooks Online.

If you have other questions or need guidance managing invoices or sales taxes in QBO, please feel free to comment below. My role is to support you in navigating these aspects of your financial management effectively.