Arch linux: custom repo: File is corrupted (invalid or corrupted package (checksum))

I created a custom repository on my manjaro machine (to make a custom Manjaro ISO) with adding:

[manjaro-mate-aur-packages]
SigLevel = Never
Server = https://github.com/FreaxMATE/manjaro-mate-aur-packages/blob/main/manjaro-mate-aur-packages/x86_64/manjaro-mate-aur-packages.db.tar.gz?raw=true 

to pacman.conf. sudo pacman -Syu runs without any issues:

:: Synchronising package databases...
 core                                       172,1 KiB   637 KiB/s 00:00 [########################################] 100%
 extra                                     1903,1 KiB  1710 KiB/s 00:01 [########################################] 100%
 community                                    6,7 MiB  1883 KiB/s 00:04 [########################################] 100%
 multilib                                   177,2 KiB  1441 KiB/s 00:00 [########################################] 100%
 manjaro-mate-aur-packages                    2,5 KiB  7,11 KiB/s 00:00 [########################################] 100%

When I try to install a package from this repo I get this error:

:: Retrieving packages...
 mate-layouts-0.0.5-2-any                     2,5 KiB  21,6 KiB/s 00:00 [########################################] 100%
(1/1) checking keys in keyring                                          [########################################] 100%
(1/1) checking package integrity                                        [########################################] 100%
:: File /var/cache/pacman/pkg/mate-layouts-0.0.5-2-any.pkg.tar.zst is corrupted (invalid or corrupted package (checksum)).
Do you want to delete it? [Y/n] 
error: failed to commit transaction (invalid or corrupted package (checksum))
Errors occurred, no packages were upgraded.

although I set SigLevel = Never. Do I have to sign the packages when creating them with buildpkg? If that is the case how do I add them to the Manjaro custom ISO? I used this doc: https://wiki.manjaro.org/index.php/Buildiso_with_AUR_packages:_Using_buildpkg and https://wiki.manjaro.org/index.php?title=Build_Manjaro_ISOs_with_buildiso