Why When i erase a late fee from an invoice, the sales tax also is being erased?

I've got some information regarding why your sales tax will be erased if you erase a late fee, LUCY76. 

In QuickBooks Online (QBO), when you erase a late fee from an invoice, the sales tax might also be erased because the late fee and the sales tax are linked to the original invoice. When you remove the late fee, it can affect the calculations associated with the invoice, including the sales tax.

The Sales Tax will be based per item. If you remove it, it will also remove the tax of your late fee. 

However, if the other line items are affected as you delete the late fee, I recommend using a private browser. This way, it will rule out any browsing history or cached files causing the problem. Here are the shortcut keys for accessing private browsers:

• Google Chrome: press Ctrl + Shift + N
• Mozilla Firefox: press Ctrl + Shift + P
• Microsoft Edge: press Ctrl + Shift + N
• Safari: press Command + Shift + N

If the issue persists, I recommend clearing your browser's cache and cookies. Also, you can use other supported web browsers that can help identify if the issue is related to your current browser. 

To learn more about late fees, you can view this guide since this contains a lot of information: Apply late fees to overdue invoices automatically in QuickBooks Online. 

Furthermore, you can record invoice payments if a customer pays an invoice. 

If you have further questions regarding late fees and sales tax, please enter your concerns in the comment section so that we can help you. Have a great day.