External HDD connection

Help me!
Hi, I installed Nextcloud on the Raspberry Pi3 +

*** Ubuntu server 18.04. LTS**
*** Nextcloud installed via the snap package.**
*** PHP 7.2.24**
*** APACHE /2.4.29**

I can’t connect an external hardisk, in Ubuntu I mounted the hdd in a folder and when I connect it to Nextcloud the green flag.
But when I upload a file it gives me the following message:
“Error while copying file to target location (copied bytes: 0, expected filesize: 467788)”

From shell I access the mounted folder and view the files present, which is not the case in Nextcloud.

thank you very much