installation on an external drive

hello, i’m new so i apologize immediately if i smoke something wrong

Help to install nextcloud with the data directory is about to start connected to the raspberry. I have ex4 formatted partition, permissions for www-data to write, write and modify. And after all, as a letter to the disk space / media / pi / nextcloud it crashes “Can’t animate save in / media / pi / nextcloud /” what am I doing wrong?

nobody, nobody has encountered such a problem ??