The issue is the result of airgap fqdn not matching or the airgap cert is different on tca manager and/or tca cp.
In the TCA Manager under Configuration we see the reason being CAS110113 and the message says:
Failed to create cluster config CR. Cluster Cluster-Name. Operation: EditCluster. Intent:
xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxx. Details: HttpStatus 422 : admission webhook
"tcakubernetescluster.kb.io" denied the request:
TcaKubernetesCluster.telco.vmware.com "Cluster-Name" is invalid: spec.airgap: Invalid value: "airgap: cannot be modified"
2.3
The following documentation can be used to update the airgap cert manually or using a script:
Update Airgap Server Certificate:
The manual method is also provided in the same document under Troubleshoot Cluster Airgap Server CA Certificate Updating if the script poses any issues.