If items are still stating “Unpaid” despite payment having been made,
this would suggest the relevant call-back or IPN (Instant Payment
Notification) settings are not in place within the sellers/payment
recipient account. Working on the assumption that payment was made
using PayPal, the seller would need to ensure they have the IPN URL
confirmed to them at Members Area > My Account > Account Settings. The
IPN would be similar to http://www.site-here.com/payment/ipn/paypal.
The IPN itself can then be setup within your own PayPal account.

more information on this is available at
https://www.tipsandtricks-hq.com/ecommerce/how-to-setup-paypal-ipn-notification-2796.
The purpose of the IPN is to notify you of a successful payment
having been made. The IPN will then automatically mark items as paid.

If you do not have an IPN set up then the you/seller must manually mark the item as being paid.