I got you with this, aashna.

There are two ways to change the message within QuickBooks Online. You can either go to the Account and Settings or Custom Form Styles. Here are the detailed steps:

Account and Settings

1. Click the Gear icon in the upper-right corner and select Account and Settings.
2. Select the Sales tab and go to the Messages section.
3. Choose the correct Sales form (Invoice, Sales Receipt, Estimate, etc.).
4. Go to the Email message field and update the content.
5. Click Save and Done.
   

Custom Form Styles

1. Click the Gear icon in the upper-right corner and select Custom Form Styles.
2. Look for the correct template. If you haven't created one, you can select Edit next to the Standard Master template.
3. Go to the Emails tab and select the correct Sales form type.
4. Go to the Standard email section and select the correct sales form type again.
5. Change the content in the Message to customer field.
6. Click Done.
   

I'll get back to you if you have more questions about this concern.