iMessage NOT syncing across iPhone and MacBook Air

ON your iPhone:

Settings

Messages

Send & Receive--> Make sure all applicable numbers and email address are selected.

Text Message Forwarding--> Make sure all applicable devices are switched ON

ON your Mac

Open Messages

In the toolbar Select Messages

In the dropdown bar, select Settings

Select the "iMessages" Tab

Make sure "Enable Messages in iCloud" is checked

Make sure all applicable numbers and emails are checked

Make sure, at the bottom of that window, that you start conversations with your phone number (Same on all devices)

Hope this helps in some way!

I wasn't sure if someone may have been using your AppleID (instead of your phone number) to contact you or you may have been using your AppleID to contact someone else...if the settings don't match up, this might have contributed to the miscommunication between your devices.

Sorry it didn't fit.