Why is when I make a invoice and save it , to add more service during the week it says paid when I save it.

Your customer may have an open credit, Marina. Let us figure this out together so you can return to your work efficiently.
 

In QuickBooks Online, there is a feature called Automatically Apply Credits. When this feature is enabled, it will automatically apply credits to open invoices, including your newly created invoices.

Let me help you turn off the Automatically Apply Credits.
 

Here's how:

1. Navigate to the Gear icon, then Account and settings.
   
   
    
2. Under Account Settings, select Advanced.
3. Click the Pencil icon in the Automation section to edit.
   
   
    
4. Turn off the Automatically apply credits feature.
5. Then Save, and then Done to apply changes.
   
   

You can check this article to know more about the feature Automatically apply credits: Create and apply credit memos or delayed credits in QuickBooks Online.  It provides a detailed overview of how the feature works.
 

Moreover, for future reference, you can check this article to identify the cause of the balance and decide what action is necessary: Resolve accounts receivable or accounts payable balances on a cash basis balance sheet in QuickBooks Online.
 

If you need more help in managing your invoices, please leave a comment below. I'm here and happy to assist you further, Marina.