Let me guide you on how to generate the partial payment of an invoice in QuickBooks Online (QBO), a_tod42.

You can achieve the one with the $50 payment as well as the outstanding balance of $50 for the $100 by creating a partial payment for an invoice. See the screenshots for your reference:

Here's how:

1. Click the + New Plus icon. 
2. Select Receive payment.
3. From the Customer dropdown, choose the name of the customer.
4. From the Payment method dropdown, select the payment method (credit card, debit, PayPal, Venmo, or ACH bank transfer).
5. From the Deposit to dropdown, select the account you put the payment into.
6. In the Amount received field, enter the amount your customer paid.
7. In the Outstanding Transactions section, select the checkbox for the invoice you're recording the payment for.
8. Enter the Reference no. and Memo if needed.
9. Press Save and close.

Once done, you can click the Print Preview or print the Partially paid invoice on the Sales page. To see the remaining balance for the customer:

1. Go to Reports (Take me there).
2. Find and open the Customer Balance Summary report.
3. Select Run report.
4. Review the customer's open balance in the Total column.

Additionally, you can utilize this article in running reports so you can have a glimpse of the financial standing of your business: Run reports in QuickBooks Online.

Please don't hesitate to hit the Reply button if you need further assistance in managing your invoices and receiving payments in QBO. I'll be right here to help you thoroughly. Take care and have a good one.