Emojis in iMessage not working!

Hi,

I have a Macbook Pro from a few years ago and although I can use the emoji keyboard, in iMessage once I type them they appear in the message with a question mark. Same goes for the emojis I receive (all emojis even supper old ones). In the message preview they appear normally, but in the actual text they won't appear without the question mark.

I've tried re-downloading the keyboard, but nothing is working and I am frustrated. This has been occurring for a few months now and I don't know what sparked it. Please help!