Why do I get an 'invalid url' error message when being redirected from Magento to PayFast?

Why do I get an 'invalid url' error message when being redirected from Magento to PayFast?

This is due to testing from a non internet accessible machine (e.g. a local development machine).

Non internet accessible machine

The module will only perform as expected if you are testing from an internet accessible machine (e.g.http://www.mydomain.co.za). It will not work from something like http://localhost or http://my.machine.local.

Ensure that you are testing on an internet accessible machine.