Configure archive folder on a network share

I'm experiencing some issues while trying to change the default log archiving location to a pre-configured network share.
The share is on a QNAP device, say \\NAS\archive.
This is what I've tried:

direct reference to the network share (in the archive settings menu, I've put "\\NAS\archive" in the textbox, after clicking on "edit")
referencing the network shared folder by mapping it to a local drive (\\NAS\archive mapped to L:) and putting the drive letter in the appropriate textbox in the archive settings menu, both with and without the trailing \ (L: and L:\)

I've tried many permissions combinations, even letting everyone read/write on the share (configured through the NAS console) and granting full control to everyone over the mapped drive.
The ELA answer was always "Not possible to create directory..." even when it was possible to write files and to create directories in the network share (mapped to a drive or not) by using Windows Explorer.
Pointing to a local folder, even if on a different drive/partition was always possible ("Directory created..." message appeared).
This thread did not help, but stated that IT SHOULD BE possible to point to a network share by mapping it to a local drive.

What am I missing?
Is there any specific procedure for the operation, besides the simple "change settings"?
Is there a particular permission schema (user+authorization) required for the share, for the folder in the remote file system, and/or for the mapped drive?

Thank you all in advance.
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Francesco Pappalardo