To make expense memos required or mandatory in CORE, you can set that option at the global level, i.e., a rule that applies across the system:

1. Go to Settings > Time & Expenses > Expense Entry.
2. Check the option Expense entry memo required. This ensures that all future expense entries won’t be accepted without a memo.
3. Click Save.

You can also set this rule at the project level:

1. Go to the Projects > General > Assignment screen.
2. Click Add Rule and select the rule Memo is required for expense entry. If required for time entries, select that option too.
3. Click Add.