This is the endpoint URI that I am sending http://<instance>/rest/v1/group/name/{group_name}/project/name/{project_name}/environment/name/{environment_name}/lineage?startTimestamp={startTimestamp}
What is {group_name}? If you are trying to use a matillion variable then it should be ${group_name}. Otherwise make sure the value of the variable is set correctly. It says the failure is from position 41 which starts at your {group_name} reference...
You mean like this? http://127.0.0.1/rest/v1/group/name/{group_name}/project/name/{project_name}/environment/name/{environment_name}/lineage?startTimestamp={startTimestamp}