I’ve read in the wiki, Supported Wireless Headsets - Phones - Documentation, that Sennheiser headsets “need Special y cord from Sennheiser (Available at Sangoma Portal Store)”. I went to the store, but none of the descriptions mention Sennheiser. Am I missing something obvious? See picture of cable store page
In the store go to “Phones” Then click on it to expand and get to “Accessories” should be the first item in the list.