To post a birthday message on Instagram: - Open the Instagram app on your smartphone. - Tap on the "+" icon at the bottom of the screen. - Select "Photo" to post a photo related to the birthday, or select "Type" to write a text message. - If you select "Photo," choose a birthday-related photo from your photo library. - If you select "Type," write your birthday message in the text field. - To add a hashtag, you can type "#" followed by a keyword. - Tag the person who is celebrating their birthday by typing "@," followed by their Instagram handle. - Once you've added your message and other details, tap "Share" to post it. - Your birthday message will now be visible to your followers and the person you tagged. - You can also add stickers, GIFs, or other Instagram features to make your birthday message more fun and interactive.