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When adding a custom parameter under configuration tab for a Custom product you cannot delete it afterwards, if you decide you no longer want that parameter. You need to delete entire product and start over.
You do not need to remove all product, simply set your custom parameter value to blank and click on Update
I did that and the parameter name still shows under the configuration tab.
Just tested this on http://demo.boxbilling.com/bb-admin.php and it works as expected.
Clicking the "Update" button next to the plugin name does NOT remove the blanked out parameters. You need to blank out the paramters and click the "Add new configuration field" button at the bottom to remove the blanked out parametrs. Very misleading.
Thats right. Will change button name to something more meaningful.