FaceTime audio not redirecting to headphones

Re:" FaceTime audio not redirecting to headphones:"

"When I make a call, the audio output won't direct to my headphones but plays through the MacBook speakers."

Am no expert in this area, yet your post deserves some response: Apple support's articles may be helpful.

FaceTime requirements on Mac - Apple Support

Eg: says:

1. Go to the FaceTime app on your Mac.
2. Click the Video menu, then do one of the following:

• Choose a specific camera.
  • Note: You can use the rear-facing camera on your iPhone as a webcam in FaceTime. See Use your iPhone as a webcam.
• Choose Automatic Camera Selection. FaceTime automatically selects a camera for you, based on whether an iPhone or other external camera is connected,
• which camera you used most recently and any app settings you’ve
  • previously chosen.
  • Choose a specific microphone or audio output device.
  • Choose Use System Setting for your microphone or audio output device.
  • If you select this option, FaceTime uses the audio devices selected in the Output pane in Sound settings. See Change the sound output settings.

If no devices are listed in the Video menu, FaceTime uses the built-in camera, microphone and speakers.

See Use the built-in camera."

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Re: "I have been into sound settings and changed the audio to headphones, which continue to play through the speakers". ... "Interestingly, when I choose my headphones in the settings and adjust the volume slider it changes the audio of the MacBook speakers".

Seems that "headphones" setting is generally used for wired headphones : ie: plugged in to your Mac:

Wondering whether the headphones are "wired" or not. ... seems may be not ?

Change the sound output settings on Mac

Eg: says:

1. "On your Mac, choose Apple menu  > System Settings, then click Sound in the sidebar. (You may need to scroll down.)
2. Click Output, then select the device you want to use in the list of sound output devices.
3. All sound output devices available to your Mac are listed, including the computer’s internal speakers, devices plugged into your computer’s sound port (), USB speakers, and AirPlay devices.
4. For any device plugged into the computer’s sound port, choose Headphones.
5. Do any of the following to adjust your sound output settings:

• Adjust the volume: Drag the Output volume slider.
• If you have Sound in the menu bar, you can turn the volume up or down from anywhere.
• To set a volume for alert sounds, drag the Alert volume slider in Sound Effects. The alert volume is relative to your computer’s volume, so if you lower the computer’s volume, alert sounds also play more quietly.
  • Stop sound output: Select the Mute checkbox.
  • Adjust the balance: Drag the Balance slider."

Seems you can play audio through one Bluetooth speaker or one set of compatible headphones at a time.

If needed: See connect a wireless accessory in the article below:

Connect accessories to your iMac - Apple Support

Thank you kindly for taking the time to reply, booragal! Good to know you were able to solve the issue! Cheers!