Invalid setting error while saving "User settings (elasticsearch.yml)"

I have following settings for all nodes in my cluster:

Inline Scripts
Scripts can be inlined in requests, e.g. search requests. We recommend disabling this, or at most enabling sandboxed. --> selected ---> Enable sandboxed inline scripts

Then I went down and under User settings that will be appended to elasticsearch.yml, I put this

script.engine.groovy.inline.search: true and click update. But it keeps throwing "Invalid settings" error. May I know what am I doing wrong, or how can I achieve what I am trying to do?

What version of ES are you using? Is there any additional information printed to the "Invalid settings" error? (Asking because I would expect the offending setting to be printed as well.)

ES 2.3.5 , I just get the popup bubble on top right corner of the "configuration" page saying "invalid settings". That's all.

"popup bubble" sounds like you are using Kibana on top of Elasticsearch?

Reading
https://www.elastic.co/guide/en/elasticsearch/reference/current/modules-scripting.html it looks like the scripting language you are trying to enable (groovy) is not a sandboxed scripting language, it also lists what other options you will need to enable to use groovy.

As an aside - may I ask what use case you are trying to solve with using groovy?

Hope this helps,
Isabel