You only pay the grafter after the work is complete.
Once you are happy with the work go back to the app and view the job. You can then select 'Pay and Close'.
Select the Days and Hour of work completed / you wish to pay. This will make the payment to the Grafter and close the job.
If you want to hire the grafter for another phase of work, then click 'Next Phase' to book another phase of work. You can them pay them again as above, when that phase is complete.