Which purpose does the parameter "ctx" have in a track request?

The event parameter "ctx=1" is sent if the clicked link leads to a page that belongs to an external domain. An external domain is each domain that is not included in "domain" in the Pixel JS configuration or "Domain" in the Tag Integration configuration.

The parameter ctx is not evaluated in the backend (it is intended for future use).

If the clicked link leads to a page that belongs to the own domain the ctx parameter is omitted ("ctx=0" will not be send). "ctx=1" is also send if the href tag contains a string with pseudo protocol, for example, href="javascript:...".