Cannot write to /boot directory No space left

[znavko]

Hi! Can you help me? My usual reconfiguratio with my usual confug now fails.

# guix system reconfigure /etc/config.scm
....
ctivating system...
making '/gnu/store/23hk1si942jxxsp85hikidhyyn3gjqws-system' the current 
system...
setting up setuid programs in '/run/setuid-programs'...
populating /etc from /gnu/store/y8jinvvspwi3r28ga6vmv38rdymg4lv3-etc...
The following derivation will be built:
 /gnu/store/wm0ci788xclkh1i3j283wn4rsbd7s4j3-install-bootloader.scm.drv

building 
/gnu/store/wm0ci788xclkh1i3j283wn4rsbd7s4j3-install-bootloader.scm.drv...
guix system: error: 
'/gnu/store/d1i6x7vwr83j1m0zms580mh2dqgx1s6m-grub-efi-2.04/sbin/grub-install 
--boot-directory //boot --bootloader-id=Guix --efi-directory //boot/efi' exited 
with status 1; output follows:

 Installing for x86_64-efi platform.
 Could not prepare Boot variable: No space left on device
 /gnu/store/d1i6x7vwr83j1m0zms580mh2dqgx1s6m-grub-efi-2.04/sbin/grub-install: 
error: efibootmgr failed to register the boot entry: Input/output error.
# mount | grep boot
/dev/sda1 on /boot/efi type vfat 
(rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)
# df -h
Filesystem Size Used Avail Use% Mounted on
none 12G 0 12G 0% /dev
/dev/sda2 47G 28G 17G 63% /
/dev/sda1 519M 152K 519M 1% /boot/efi
tmpfs 12G 119M 12G 1% /dev/shm
none 12G 24K 12G 1% /run/systemd
none 12G 0 12G 0% /run/user
cgroup 12G 0 12G 0% /sys/fs/cgroup
none 12G 0 12G 0% /var/cache/fontconfig
tmpfs 2.4G 16K 2.4G 1% /run/user/1000
/dev/sdc2 227G 3.5G 212G 2% /mnt
I see that "//boot" is using -- with two slashes.
Is it a bug?
Ps: this happened after I installed Debian on /dev/sdc