If you want to make your field require an input, enter the template editor of your template.
Locate the field you wish to make mandatory and click on the pencil icon.
Once the element details appear click the Yes radio button under Mandatory Field.
Once selected click on Save changes. The field will have a red asterisk next to it indicating it is mandatory.
The client will not be able to submit their engagement unless this field in the template is filled in with data.