If you've upgraded your account, the new receipt may show up in red as UNPAID up to 1-2 hours due to a delay in the payment processor. Check back in a couple hours to be sure payment successfully processed and you'll see a green PAID icon.
When downgrading, your most recent receipt may be marked as UNPAID and also may take up to 1-2 hours to process. Once it's successful, your account will be credited the difference of the initial plan price you were on and the new plan price for the plan you just selected. Any positive account balance will be applied on your next billing cycle.