Cannot partition w/ Boot Camp Assistant on macOS Mojave

The problem is called overallocation. The following helped me to fix it on Mojave APFS:

Please note, there is a lot of posts out there telling you to do fsck. If you are on APFS you need to do fsck_apfs instead. This is what made the difference for me.

1. Shut down your Mac.
2. Start and hold Cmd-S to boot into single user mode.
3. Run fsck_apfs -o
4. It will ask you to confirm, type in y and press Enter.
5. When finished (up to 3 minutes) type reboot and press Enter.

After trying everything I could find, this finally worked.

I also ran fsck_apfs -n -l before I ran fsck_apfs -o but I don't think that made any difference.

As I watched the results it produced this line: Overallocation detected on Main device And then it did: Fix overallocation

The secret trick was running fsck_apfs -o -y. 🤷🏻‍♂️

I had the same problem , i did reinstall mac os (Mojave) but problem not resolved. Finally i solved using this.

• Restart your mac and Pressed Command + S to boot into single user mode.

• Type fsck_apfs -y /dev/disk0s2 and hit enter

• If you can see some questions type y and hit enter

• After all you can see like as appear OK

• Type reboot and hit enter

  your problem is solved !