How do i force a field to be required
There isn't a way to do this in the user interface but you can write a small extension where you either:

Use https://docs.civicrm.org/dev/en/latest/hooks/hook_civicrm_buildForm/ and change the field definition so that it's required.
Use https://docs.civicrm.org/dev/en/latest/hooks/hook_civicrm_validateForm/ and set an error if the field is blank.