Simple URLs is a free plugin for complete url management of WordPress website. It is ideal alternative to now outdated GoCodes plugin. You can install it like any other plugin and start creating redirected affiliate urls, for example: xyz.com/products/123.html can be redirected using yourblog.com/go/123/ URL.
Why links of Simple URLs show ‘page not found’ error: Ideally, this plugin should work without any issue. However, if you had changed permalinks structure after “Simple URLs’ plugin install – then “page not found” error may appear. To fix it, just goto Settings > Permalinks in your WordPress dashboard and click Save Changes button. Now it should start working.
If it still does not work, implies conflict with other plugins. You can disable all plugins to check the functionality of “Simple URLs” plugin.