<p>I am using K8s ManagedCertificate to create a certificate on GCE. I wanted to add a new subdomain to my cert, so update the yaml file and did kubectl apply. I tried to describe my cert to see if everything is ok but found an error</p>
<pre><code>Warning  BackendError  16m (x144 over 36h)  managed-certificate-controller  googleapi: Error 400: The ssl_certificate resource '&lt; redated &gt;' is already being used by '&lt; redated &gt;', resourceInUseByAnotherResource
</code></pre>
<p>Also in the describe I don't see the new sub domain I am trying to add as active.</p>
<pre><code>Spec:
  Domains:
    web.sub1.domain1.com
    web.sub1.domain2.com
    web.newsub.domain2.com
    web.sub2.domain2.com
    web.sub1.domain3.com
Status:
  Certificate Name:    &lt; redated &gt;
  Certificate Status:  Active
  Domain Status:
    Domain:     web.sub1.domain1.com
    Status:     Active
    Domain:     web.sub1.domain2.com
    Status:     Active
    Domain:     web.sub2.domain2.com
    Status:     Active
    Domain:     web.sub1.domain3.com
    Status:     Active
  Expire Time:  2021-07-30T00:54:02.000-07:00
</code></pre>

<p>As John Hanley mentioned you can't update SSL cert. <a href="https://cloud.google.com/compute/docs/reference/rest/v1/sslCertificates#methods" rel="noreferrer">Google API for SSL cert doesn't have an update method</a>. So deleted the resource using <code>kubectl delete -f &lt;cert&gt;.yaml</code> and created it again with <code>kubectl apply -f &lt;cert&gt;.yaml</code> and it worked</p>
