File permissions

Errors which say Something happened, Unable to create, or Unable to write are caused by lack of permission. Your server user-name is usually www-data or sometimes apache.

To fix this error do all of the steps, in order.

1. Which server do you use: Apache, Nginx, Windows? Please find the configuration file. See what "user name" it runs things as. You can discover this by searching the web server config file for "user" and "group". Confirm that it is www-data. Or go list your files to see the group name and owner name ls -l /var/www/html/matomo/tmp
2. sudo chown -R www-data:www-data /var/www/html/matomo # I am assuming www-data was found in Step 1
3. sudo find /var/www/html/matomo/tmp -type f -exec chmod 644 {} \;
4. sudo find /var/www/html/matomo/tmp -type d -exec chmod 755 {} \;
5. sudo find /var/www/html/matomo/tmp/assets -type f -exec chmod 644 {} \;
6. sudo find /var/www/html/matomo/tmp/assets -type d -exec chmod 755 {} \;
7. sudo find /var/www/html/matomo/tmp/assets -type f -exec chmod 644 {} \;