500 Internal Server Error -> sent keycloak httpPost request -> role-mappings/realm

I send HTTPPOST
http://127.0.0.1:8080/admin/realms/SBMS/users/b6b095f2-a182-4258-a92b-f34cd89c2c1d/role-mappings/realm (with exisiting userid b6b095f2-a182-4258-a92b-f34cd89c2c1d)
header
Authorization : Bearer … (with existing Bearer token)
Content-Type : application/json
Body
id : 30700624-f128-4393-b898-845ad1c5ec40 (with existing role id)
name : sbmsOperatorRole (with existing role name)

and get allways an ERROR 500 Internal Server Error

ps : with keycloak-19.0.1 and Windows 10
ps : Keycloak Rolle: sbmsOperatorRole and USERID : b6b095f2-a182-4258-a92b-f34cd89c2c1d
are created
ps : with these configuration (token and userid) i had do e.g creating an RalmRole → therfore it goes