Can't mount external hard disk on nextcloud ubuntu application(A dependency job for var-snap-nextcloud-common-nextcloud-data.mount failed.)

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I have been trying to mount a external hard disk on my nextcloud application through systemd. everything goes well till i run it. I get the error:

A dependency job for var-snap-nextcloud-common-nextcloud-data.mount failed.

I created a file in this directory:

/writable/system-data/etc/systemd/system/var-snap-nextcloud-common-nextcloud-data.mount

The configuration looks like this:

[Unit]
Description=Mount unit for data1

[Mount]
What=/dev/disk/by-label/9e5dfd97-c7d5-4b52-8736-d50bc2893c30/sda1
Where=/var/snap/nextcloud/common/nextcloud/data
Type=ext4

[Install]
WantedBy=multi-user.target

does someone know what i do wrong?