What version of Parrot are you running? (i4.4 , Parrot Security)
What method did you use to install Parrot? (parrot-experimental)
Configured to multiboot with other systems? (yes)
For those who are trying to make the manual partitionning method, I think you need to just set two partiton; one for the root file system (ext4 or btrfs) and a swap partition. After the system installation, the system installation pogram will ask you where you want install the grub bootloader.
That’s what i tried and it’s worked for me.