As @PiotrP.Karwasz says no write permission for the group.

Solutions:

• give write permission to the group: chmod g+w -R /path/to/folder
• give write permission to the user: as you did, but don't switch it back.
• give write permission to (possibly many) additional users/groups: using setfacl see What are the different ways to set file permissions, etc., on GNU/Linux?

As @PiotrP.Karwasz says no write permission for the group.

Solutions (one of):

• give write permission to the group: chmod g+w -R /path/to/folder
• give write permission to the user: as you did, but don't switch it back.
• give write permission to (possibly many) additional users/groups: using setfacl see What are the different ways to set file permissions, etc., on GNU/Linux?