OnePlus 1 - can not install android 9


I can not install Android 9 on my Oneplus One. Here are the problems:

at step 7. after entering " fastboot oem unlock" it says: OK (0.010s). Finished . Total time: 0.010s

and nothing happens on the Oneplus One. The screen just displays “Fastboot Mode” and I can not proceed to step 9. There is no “Bootloader menus” to select “Start”.
Please advise what to do.