Your VISA Application will show as incomplete until you have finished all parts of the VISA Application and paid all the fees for the VISA.
You can see which parts of the process have not been completed by going to Your Profile > VISA Applications and checking which sections do not have a green tick indicating that they have been completed.
You can find all fees payable by you by going to Your Profile > VISA Applications > Payments.
Please note that you might have an OPTIONAL fee for a Priority VISA Application. This does not have to be paid for the application to be completed, but if you want a priority processing time you can choose to pay it in addition to the required fees.