Discounts and payments are not being calculated, bugs in UK

Thanks for reaching out to the Community forum, @ssresourcecentre.

QuickBooks Online (QBO) does have an automatic feature such as automatically applying payments to an invoice. This feature might be turned on, which results from the payment applying to the old invoice.

To check, here's how:

1. Go to the Gear icon at the top.
2. Select Account and Settings.
3. Choose Advanced on the left of the screen.
4. Go to the Automation section.

If it's turned on, that's causing the issue. If you wish to turn it off, continue with the steps below:

1. In the Automation section, select the Pencil icon.
2. Toggle to turn off Automatically apply credits.
3. Select Save.
4. Click Done.

To know how to receive and categorize invoice payments, see this article for a guide: Record invoice payments in QuickBooks Online.

Post again in the Community if you have additional concerns. I'm here to keep helping. Have a good one!