Permission denied to access external drive

I have a ROCK installed on a intel NUC i7 with an attached external usb SSD.

I am trying to drop music files into the SSD via my network. I can connect to ROCK as a a guest via MAC OS Finder and see the SSD. When I try to add files to the drive I get a permission denied message. I have been able to do this successfully in the past.

Has there been any changes to MAC OS or ROON that might effect this? Or does anyone the right way to do this? Thanks for any help.

If the external drive on the ROCK NUC is HFS+ format, then you cannot write anything to it.

The drive is formatted as OS Extended (Journaled). What format is recommended please? Thanks.

Thank you, thats very helpful!