The mentioned documentation on posty-soft.org isn't accessible because there is a downgrade of security (https to http).
For example a current version of Chrome will give you the following output:
Mixed Content: The page at 'https://www.posty-soft.org/swaggerv2/posty_api.html' was loaded
over HTTPS, but requested an insecure XMLHttpRequest endpoint
'http://posty-api.herokuapp.com/api/v1/swagger_doc.json?auth_token=123456'.
This request has been blocked; the content must be served over HTTPS.
The mentioned documentation on posty-soft.org isn't accessible because there is a downgrade of security (https to http). For example a current version of Chrome will give you the following output: