I use the Revit API in 2018 and 2019 for the installation of a new shared parameter to the project.
Installation takes place normally for all categories of Revit, except one - Stairs Support.
When you try to set a parameter in the project for this category, an error occurs:
Binding the parameter to the category Supports is not allowed
at Autodesk.Revit.DB.BindingMap.Insert_(Definition key, Binding item, Object nullableParamGroup)
This error occurs for the following reason: the AllowsBoundParameters property (http://www.revitapidocs.com/2019/7bdf1bee-41ce-45e0-9f00-7c1efa49a502.htm) is a pointer to whether a parameter can or cannot be set for a particular category.
If its value is "True", it means that you can set the project parameter via the API. For the «Supports» category, the property value is set to "False".
Revit, in turn, sets the parameter for this category without problems, and therefore relies on its internal installation rules.
The solution is to fix the property value to "True" at the Revit API level.