The query parameter 'deserializeValue' of the REST URL "/process-instance/{id}/variables" has no effect, the returned process variables are deserialized in any case. Same applies for the REST URL "/task/{id}/variables".

The cause is a wrong parameter name in the OpenApi specification openapi.json (from archive: camunda-engine-rest-openapi-7.13.0.jar). Line 9793 and line 14841: the variable is exptected to be 'deserializeValues' (not 'deserializeValue'). Therefore the decoding of the query parameters goes wrong.

Note that the documentation is correct:

https://docs.camunda.org/manual/7.13/reference/rest/process-instance/variables/get-variables/

https://docs.camunda.org/manual/7.13/reference/rest/task/variables/get-task-variables/