Customise your tasks to set the notes field or attachments as requirements for being able to mark a task as completed.
To choose this option for a task, head to the task's customisation page. You can find this by clicking into the task as if you were going to complete it, and then selecting the 'Customise task' option from the right hand menu.
You will then see a selection of settings you can configure. These are individual to this particular task. Make sure you have checked the box for notes and/or uploads before clicking the green button to save and update your chosen settings.
