"Kindly be advised" is another way of saying "just a friendly reminder." It maintains a polite and gentle tone while conveying the same message. Other alternatives could include:
- "Gentle nudge"
- "Polite heads-up"
- "Courteous prompt"
- "Helpful alert"
- "Considerate notification"
- "Amicable notice"
- "Thoughtful reminder"
- "Cordial update"
- "Informal friendly recall"
- "Neighborly memo"
Choose the one that best suits the context and tone of your message.