To ensure a field is populated on every record without exception, an administrator should make the field "Universally Required." This setting is enforced at the system level, meaning a value is required whether the record is created or updated through the user interface, an API call, or a data import tool. This is the most comprehensive way to enforce a mandatory field requirement across the entire Salesforce platform for that specific object, aligning perfectly with the need for the Billing System field to be filled on every Invoice record.

B. Create a Process Builder to set the field.

Process Builder is an automation tool used to perform actions, not to enforce data entry rules for users. It cannot make a field mandatory.

C. Define an approval process for the child.

Approval processes are designed for formal record review and approval sequences, not for enforcing field-level data integrity upon record creation.

D. Require the field on the record type.

Requiring a field via a page layout (associated with a record type) only enforces the rule when users interact with that specific layout in the UI. It does not enforce the requirement for records created via the API or other system processes.

1. Salesforce Help Documentation

"Custom Field Attributes":

In the field creation wizard

the "Required" checkbox is described as: "Always require a value in this field in order to save a record. This is also known as a universally required field." This directly supports making the field universally required to ensure it is always filled.

2. Salesforce Help Documentation

"Considerations for Universally Required Fields":

This document clarifies the scope of the setting: "A universally required field is automatically added to all page layouts... The field is also required for records created with Quick Create

a related list

or the Salesforce API." This confirms that making a field universally required is superior to making it required on a page layout (Option D) when the rule must apply to all record creation methods.

3. Trailhead

"Data Modeling" Module

"Customize a Salesforce Object" Unit:

This official training module explains the field creation process. When detailing field properties

it instructs administrators to "Select Required to make this a mandatory field. Users must enter a value before they can save the record." This establishes the "Required" checkbox as the standard method for this requirement.