Group attribute externalId is not passed when using push groups to app function (SCIM)

Questions SCIM
1

Hello,

I would like to receive the externalId of a group in my custom app integration with SCIM. When I am trying to add this id to the group attributes I get the following error:
Property name externalId is reserved for use by external directory groups.

I have added the group via Directory → Groups → Add Group.

While debugging I do get some information like the displayName and description when pushing the groups. However I do not get the externalId.

Am I using the wrong group or what actions should I take to get this to work?

Thanks in advance!