If your plugin call text is shown unchanged, i.e. something like this:
{payage "green widget" 6.50 GBP}It could be that the Payage Plugin is not installed, or it is not enabled in the Joomla Plugin Manager. The Payage Plugin must be downloaded and installed separately from the component and then enabled in the Joomla Plugin Manager.
If the Plugin is installed and enabled, but still not working properly, view your article in HTML mode. Some wysiwyg editors make a real mess of things. For example:
{payage<br /> "green widget" 6.50 GBP}If you can't get the article to save cleanly, you might need to change your default editor to "Editor - None" in Joomla Global Configuration.
If your plugin call text works ok when used in an article, but not when used in a Custom HTML Module, the reason is that you did not enabled the Prepare Content option in the Module options. This option tells Joomla to process plugins embedded in the content. If this option is set to "No", plugins are not processed. You must set this option to "Yes".
If you use the plugin in form mode, you may experience problems if you have System Cache switched on in Joomla Global Configuration, or if you have enabled the Joomla System Page Cache plugin. Problems arise because Joomla does not take the form data into account when deciding whether to serve the article from the cache or to re-generate it. If the article is served from the cache, the plugin does not get called and cannot do its job. If you use the plugin in form mode, you cannot use Joomla caching, although some third-party caching extensions might work.
If you have an editor or an extension that provides an article preview mode in the back end, it probably will not process article plugins. Check the article in the front end.