NixOS Installation failed

Hello NixOS-Community,

today I tried to install NixOS the second time on my computer. The first time I had problems with partitioning my disk and did the installation completely manually. But the OS did not show up in my BIOS to boot nor did it install grub.
The second time I got the following error
Failed to activate swap: /dev/mapper//dev/sdc3

Full installer log:

How can I fix this issue and install NixOS?