Yes it is a permission issue. Login to your Droplet via SSH as the root user and execute the following command:

chown -R www-data:www-data /var/www

To expand on the answer provided by @jesin , what chown does is simply change ownership. The -R tells chown to recursively change ownership of all files & directories in the path specified, starting from the endpoint and ending when there’s nothing more to change.

Using his example,

chown -R www-data:www-data /var/www

… starting with www, all files & directories will now be owned by the user:group www-data. In the event you don’t want www to be owned by this user and group, you could use:

chown -R www-data:www-data /var/www/*

In most cases, I keep the first two directory locations owned by root or another non-privileged user (better option) to prevent directory traversing by other system users.

If you’re hosting your content in another directory, simply swap /var/www/ with the system path you’re using. From the CLI, you can get the full path by using:

echo $PWD