When opening an HTTP service to a Siemens LOGO! via the Portal, the following error is displayed:

502 Bad Gateway

In some circumstances, the following error can also be observed in the network log of your browser's development tools (F12):

Uncaught TypeError: Cannot read properties of undefined (reading 'trim')

The Siemens LOGO! is a PLC with limited capabilities. One of the biggest limitations is that it can only handle up to 5 simultaneous TCP streams at a time, which is equivalent to a single web browser session. In other words, only one user can view the HTTP server at a time. This applies not only to the use of HTTP service, but also to accessing it over VPN and even locally.

It is possible to use a Siemens LOGO! with an HTTP service only if the following requirements are met:

1. The Siemens LOGO! is running firmware 1.83.2 or higher.
2. The Siemens LOGO! is configured to serve its web interface via HTTPS.
3. Only one user is accessing the HTTP server at a time, whether over an HTTP service, VPN, or locally.