The description, amount, and currency parameters can be specified as variables by preceding them with an underscore, in which case the plugin tries to find Get or Post variables to resolve the parameters. For example:
{payage _item _price USD}In this example the plugin tries to find Get or Post variables named "item" and "price". If they are found and valid, their values are used to generate the payment buttons. If they are not found or invalid, an error message is shown in place of the plugin call.