You are using a SQL Server Integration Services (SSIS) project that is stored in the SSIS catalog. An Environment has been defined in the SSIS catalog. You need to add the Environment to the project.

catalog.set_environment_reference_type modifies the type (relative or absolute) of an environment reference that already exists; it cannot create a new reference.

catalog.set_environment_property sets a property such as the description of an Environment object itself, and does not associate an Environment with a project.

catalog.create_environment_reference creates a reference between a deployed SSIS project and an Environment in the SSISDB catalog, which is the required step to make the Environment's variables available for mapping to project or package parameters.

catalog.create_environment creates a brand-new Environment folder object in the catalog; since the Environment already exists, this procedure is not needed and would not link it to the project.