Check your Json_Structure file and ensure the json message is fully copied to Json Snippet. I guess that you have mis-typo in that field.
It looks like a wrong teamcenter configuration in your mendix app.
Please make sure that you are use the correct settings:
Configuration Name (name of your choice): e.g. Mendix4TC
Teamcenter Host Address (tc 4-tier server URI): e.g. http://[hostname]:[port_webserver]/[tc_name]
Teamcenter FMS URL: e.g. http://[hostname]:[port_FMS]
Active: select yes :)