I've incorrectly added payments to invoices, how do I remove payments. Tried to delete invoice entirely but it now says the customer owes me money & subtracts the sum

Hello and welcome to the Community, poppinplumbing-o

We'll be happy to share some insight on deleting customer payments in QuickBooks Online. 

To delete, simply go to Customers (Take me there) and select the relevant customer from the list. Then, scroll down the Transaction list to locate the payment (or use the Type drop-down to filter the transaction list to show only Money received).

Once you have located the payment, select the drop-down beside the transaction in the Action column and click Delete.

When you delete the payment, this will correct the negative (credit) balance that you currently have on the customer account.

Thanks for reaching Intuit QuickBooks support on the Community today. If you need any further help, please get back in touch.