An entry for a swap device in the /etc/vfstab file contains the following:
The full path name of the swap slice or swap file on system with a UFS root file system or a swap volume path name on a system with a ZFS root file system
File system type of the swap slice or swap file
The file system that contains a swap file must be mounted before the swap file is activated. So, in the /etc/vfstab file, ensure that the entry that mounts the file system comes before the entry that activates the swap file.