Can't boot into bootloader on Oppo F1s

I can't get into fastboot mode on my Oppo F1s (A1601), Android 5.1. Here is what I'm doing: - adb and fastboot are installed on Mac - I have developer options and OEM unlock enabled - In the terminal, adb devices shows my phone - I enter adb reboot-bootloader but it does not say "fastboot mode" on the screen like I have read it is supposed to. It just restarts my phone. (note I have tried variations like reboot_bootloader; same result) Am I doing it wrong or is fastboot not on this phone? Or is it hidden somehow? The solution should be Mac supported, also I have windows 10 on a virtual machine.