Yes the UUID is correct. 61387973-32fd-4fe0-8326-0966a1a62008
well done! 
that was important.
so now run the following command:
sudo mount --all
which will mount that device
then issue the following command and post the output here
sudo ls -al /mnt/nextcloud
wpender@tank:~$ sudo ls -al /mnt/nextcloud
total 8
drwxr-xr-x 2 root root 4096 May 6 19:07 .
drwxr-xr-x 5 root root 4096 May 6 19:07 ..
should be www-data:www-data
that is correct, well done!
now enter the following command to enable external media in snap
sudo snap connect nextcloud:removable-media
now go to nextcloud GUI → files external → connect local device /mnt/nextcloud → be happy! 
okay, sorry I´m not familiar with snap.
no problem… thanks for your help anyway
I am on external storage but I do not see connect… sorry
@wpender the reason you couldn’t get that drive connected is because your permissions were not correct. the docs repeat it constantly:
What permissions should external media have?
See FAQ’s and Snap confinement
Removable media or external storage must be mounted to either
/mediaor/mntas root with root permissions and connected to Snap!
so if you create that mount point as root with root permissions, the snap will be able to access the device.
don’t be sorry, try try again… you’ll get it right eventually
you must now add the storage to your Nextcloud instance.
okay its connected but it says 0kb is this because there is nothing in there right now?
check the points: ext.drive is formated as ext4, mounted in your specify lokation
