Update index pattern fields via Kibana REST API fails

[mpjjonker (Michel Jonker)]

Hi
We are using Kibana version 7.17.
When I follow the instructions here (Update index pattern fields API | Kibana Guide [7.17] | Elastic) to update fields via the REST API , I get the error

[request.body.fields]: defintion for this key is missing

These are the request details:

curl --location --request POST '<KIBANA_HOST>/api/index_patterns/index_pattern/df51c920-a6a0-11ec-a5d1-87582857b04a#/fields/' \
--header 'Authorization: ApiKey xyz' \
--header 'kbn-xsrf: true' \
--header 'Content-Type: application/json' \
--data-raw '{
    "fields" : {
        "objectid": {
            "count": 100
        }
    }
}

Get requests on this endpoint do work , we get al the fields in the indexpattern.

[mpjjonker (Michel Jonker)]

Tsss
Somehow there is a # added after the index-pattern ID.
When I remove this character, it works !