Adding kubernetes cluster - problem authenticating with your cluster

Trying to get kubernetes cluster linked to Gitlab to test CI.

Following the instructions here, but get the following:

There was a problem authenticating with your cluster. Please ensure your CA Certificate and Token are valid.

I’ve tried deleting the cluster and setting up again (suggested here) - but this hasn’t made a difference.

Using the same $TOKEN, the following curl command works fine from another machine

curl -X GET $APISERVER/api --header "Authorization: Bearer $TOKEN" --insecure

So it looks like it’s something to do with the CA Certificate. Any help would be appreciated.