https://www.theverge.com/2018/8/27/17786428/samsung-gear-vr-adapter-free-galaxy-note-9-buyer

Samsung is offering Note 9 owners free Gear VR adapters so that they can use the most recent model of Samsung’s virtual reality headset with the company’s latest smartphone. If you own both the Note 9 and Gear VR with Controller, the new USB Type-C adapter can be obtained by calling 1-800-Samsung.

The Note 9’s “increased size” has led to compatibility issues with last year’s headset, according to Samsung. The display is only 0.1 inches bigger than the Note 8, but those slightly larger dimensions are enough to cause a problem. The headset will fit the Note 9 once the adapter is inserted.