I want delete label from a node or a pod by kubernetes API, my kubernetes version:1.24

kubectl get pod --show-labels | grep all-flow-0fbah
all-flow-0fbah      1/1     Running   2        9d      app=all-flow,op=vps1,version=1001

I use command as below:

 curl --request PATCH --header "Content-Type:application/json-patch+json" http://10.93.78.11:8080/api/v1/namespaces/default/pods/all-flow-0fbah --data '{"metadata":{"labels":{"a":"b"}}}'

But this doesn't work. Return message as below:

{
  "kind": "Status",
  "apiVersion": "v1",
  "metadata": {},
  "status": "Failure",
  "message": "the server responded with the status code 415 but did not return more information",
  "details": {},
  "code": 415
}

Then I change the curl header like this :

curl --request PATCH --header "Content-Type:application/merge-patch+json" http://10.93.78.11:8080/api/v1/namespaces/default/pods/all-flow-0fbah --data '{"meadata":{"labels":{"op":"vps3"}}}'

It not delete label but add a new label to that pod. So is there any one can tell me how to delete a label for a pod like use command :

kubectl label pod all-flow-0fbah key-

Thanks!