This is the 3rd plex topic in as many days - if I only knew what plex was I might be better at answering this question.
What are the permissions of the target folder:
comment = test share
path = /home/share
read only = no
browseable = yes
guest ok = yes
create mask = 0755
You have a share that allows write by anyone but samba cannot override Linux permissions on the shared folder itself.
If you just created the folder and then shared it the permissions might be something like this:
The only person who has write access is the owner of the directory and it's probably root so the guest will never gain write access.
One way is to change permissions to drwxrwxrwx by doing this:
sudo chmod 777 /home/share