Hello, davidfromsydenham. Thank you for posting to the Apple Support Communities. We understand the situation you are noticing when starting FaceTime calls on your Macbook. We know that staying connected with your contacts must be important to you, and we’re happy to help research any possible solutions here.
From what we gather, you are noticing this issue only with one device that you use with your FaceTime and Apple ID accounts. In a situation like this, there are several troubleshooting steps that we would suggest starting with. Please complete each step in the following Apple Support article before testing FaceTime calls again on your Mac:
If FaceTime isn't working on your Mac - Apple Support
If you continue to notice the same issue after completing the troubleshooting steps above, we can help you more. A problem like this could be related to the network that you are using. To find out more, can you tell us if you are able to make FaceTime calls normally after connecting your Macbook to a different connection?
Does this also only seem to be an issue with certain contacts that you call using your Macbook? Or does this happen with all contacts that you attempt to FaceTime with?
We hope that these troubleshooting steps help you and we look forward to your reply.
Have a great day!