Nextcloud version (eg, 12.0.2): 16.0.6
Operating system and version (eg, Ubuntu 17.04): Ubuntu 18.04.3 LTS
Apache or nginx version (eg, Apache 2.4.25): nginx version: nginx/1.14.0 (Ubuntu)
PHP version (eg, 7.1): 7.2
The issue you are facing:
I keep getting a 404 on the site. I originally just had a blank screen so I have changed the php version and now I get a 404 with index.php file not found
The output of your Apache/nginx/system log in
2019/11/23 19:27:02 [error] 903#903: *4558 "/var/www/sync/index.php/index.php" is not found (20: Not a directory), client: my.ip.address, server: sync.mywebsite.co.uk, request: "GET / HTTP/2.0", host: "sync.mywebsite.co.uk"