For me below curl commands works:
commands:
curl -X POST https://keycloak.local/admin/realms/opendesk/clients/<realm-management-id>/authz/resource-server/policy/client \
--header "Authorization: Bearer ""$MASTER_TOKEN" \
--header "Content-Type: application/json" \
--data '{"clients":["<id-of-client>"],
"logic":"POSITIVE",
"name":"<name-of-policy>",
"description":"<description>"}'
Output/Response:
{"id":"baedXXXX-XXX-XXXX-XXXX-2c72b304f7a3","name":"<client-id>","description":"","type":"client","logic":"POSITIVE","decisionStrategy":"UNANIMOUS","clients":["<id-of-client>"]}