One workaround is:

1. connect to your server
2. change into postgres user sudo su - postgres
3. open psql terminal with your database (psql [database name])

4. write sql command:

   update hr_payslip set state = 'draft';

that sets all the existing payslips into draft after that you can delete them. If you don't want to set all the payslips into draft you can add there condition:

where id=[id of the payslip you want to set into draft]

This condition has to be put before semicolon (";").