Thanks for the suggestion Grzegorz.

I've experimented with changing the php.ini and nginx setting like you mentioned.

upload_max_size was turned up to 4 mb
post_max_size was set to 8mb


I restarted the PHP-fpm and nginx server and got the same message but with the updated value "An unrecoverable error occurred. The uploaded file likely exceeded the maximum file size (4 MB) that this server supports."

nginx setting client_max_body_size seems to have no effe t either.

I think I have address the "Undefined index" situation, do you have any clues?

Thanks!

Jonny