Can't get passed admin creation screen

Steps to reproduce
1. Installed Owncloud on my Raspberry PI using this tutorial https://pimylifeup.com/raspberry-pi-owncloud/
2. Visited 192.168.1.100 in chrome and saw the "create and admin account" screen for owncloud.
3. Filled in the form and tried to submit
4. The page refreshes and the form is empty

Expected behaviour
I guess it should have created my admin account and showed me the logged in view

Actual behaviour
Nothing happens, the page just refreshes. No error messages

Server configuration
Operating system: Raspberry PI, Raspbian GNU/Linux 8 (jessie)
Web server: Nginx
Database: Mysql
PHP version: PHP5
ownCloud version (see ownCloud admin page): owncloud server 9.1
Updated from an older ownCloud or fresh install: Fresh
Special configuration (external storage, external authentication, reverse proxy, server-side-encryption):

ownCloud log (data/owncloud.log)

Please paste possible errors in the following code block, see https://central.owncloud.org/t/how-to-find-webserver-or-oc-logfile-enable-php-logfile/808 for more info

{"reqId":"g9o4tRu40uTypUsD2nJ3","remoteAddr":"192.168.1.170","app":"PHP","message":"Automatically populating $HTTP_RAW_POST_DATA is deprecated and will be removed in a future version. To avoid this warning set 'always_populate_raw_post_data' to '-1' in php.ini and use the php:\/\/input stream instead. at Unknown#0","level":3,"time":"2017-03-08T14:09:33+00:00","method":"POST","url":"\/index.php\/heartbeat","user":"--"}
{"reqId":"U38bEo0I1nZcA5ZVaEwL","remoteAddr":"192.168.1.170","app":"PHP","message":"Automatically populating $HTTP_RAW_POST_DATA is deprecated and will be removed in a future version. To avoid this warning set 'always_populate_raw_post_data' to '-1' in php.ini and use the php:\/\/input stream instead. at Unknown#0","level":3,"time":"2017-03-08T14:24:36+00:00","method":"POST","url":"\/index.php\/heartbeat","user":"--"}
{"reqId":"MR1qpPDGAFalUSlbuZtK","remoteAddr":"192.168.1.170","app":"PHP","message":"Automatically populating $HTTP_RAW_POST_DATA is deprecated and will be removed in a future version. To avoid this warning set 'always_populate_raw_post_data' to '-1' in php.ini and use the php:\/\/input stream instead. at Unknown#0","level":3,"time":"2017-03-08T14:39:42+00:00","method":"POST","url":"\/index.php\/heartbeat","user":"--"}
{"reqId":"swDAZH3cguuMaRwqzNcP","remoteAddr":"192.168.1.170","app":"PHP","message":"Automatically populating $HTTP_RAW_POST_DATA is deprecated and will be removed in a future version. To avoid this warning set 'always_populate_raw_post_data' to '-1' in php.ini and use the php:\/\/input stream instead. at Unknown#0","level":3,"time":"2017-03-08T14:54:51+00:00","method":"POST","url":"\/index.php\/heartbeat","user":"--"}
{"reqId":"vBGyTLdSoOeHU8ILhMHu","remoteAddr":"192.168.1.170","app":"PHP","message":"Automatically populating $HTTP_RAW_POST_DATA is deprecated and will be removed in a future version. To avoid this warning set 'always_populate_raw_post_data' to '-1' in php.ini and use the php:\/\/input stream instead. at Unknown#0","level":3,"time":"2017-03-08T15:09:54+00:00","method":"POST","url":"\/index.php\/heartbeat","user":"--"}
{"reqId":"XahO7Sllb8bjv3cerX9A","remoteAddr":"192.168.1.170","app":"PHP","message":"Automatically populating $HTTP_RAW_POST_DATA is deprecated and will be removed in a future version. To avoid this warning set 'always_populate_raw_post_data' to '-1' in php.ini and use the php:\/\/input stream instead. at Unknown#0","level":3,"time":"2017-03-08T15:25:05+00:00","method":"POST","url":"\/index.php\/heartbeat","user":"--"}
{"reqId":"hWSN7rP5SLXQyOBCQeoh","remoteAddr":"192.168.1.170","app":"PHP","message":"Automatically populating $HTTP_RAW_POST_DATA is deprecated and will be removed in a future version. To avoid this warning set 'always_populate_raw_post_data' to '-1' in php.ini and use the php:\/\/input stream instead. at Unknown#0","level":3,"time":"2017-03-08T15:40:06+00:00","method":"POST","url":"\/index.php\/heartbeat","user":"--"}
{"reqId":"TFV7IXJG7HV9FFcq8Erz","remoteAddr":"192.168.1.170","app":"PHP","message":"Unknown: POST Content-Length of 199 bytes exceeds the limit of 2 bytes at Unknown#0","level":3,"time":"2017-03-08T15:41:29+00:00","method":"POST","url":"\/index.php","user":"--"}
{"reqId":"AkDfXSyTi79QOH0Uoi4B","remoteAddr":"192.168.1.170","app":"PHP","message":"Unknown: POST Content-Length of 207 bytes exceeds the limit of 2 bytes at Unknown#0","level":3,"time":"2017-03-08T15:42:39+00:00","method":"POST","url":"\/index.php","user":"--"}
{"reqId":"DVcKA7SiRodkdGCui6fK","remoteAddr":"192.168.1.170","app":"PHP","message":"Automatically populating $HTTP_RAW_POST_DATA is deprecated and will be removed in a future version. To avoid this warning set 'always_populate_raw_post_data' to '-1' in php.ini and use the php:\/\/input stream instead. at Unknown#0","level":3,"time":"2017-03-08T15:57:47+00:00","method":"POST","url":"\/index.php\/heartbeat","user":"--"}
{"reqId":"xj4O9\/00Wx3K1gEsyCo6","remoteAddr":"192.168.1.170","app":"PHP","message":"Automatically populating $HTTP_RAW_POST_DATA is deprecated and will be removed in a future version. To avoid this warning set 'always_populate_raw_post_data' to '-1' in php.ini and use the php:\/\/input stream instead. at Unknown#0","level":3,"time":"2017-03-08T18:25:10+00:00","method":"POST","url":"\/index.php\/heartbeat","user":"--"}
{"reqId":"2Y5nQBhk7kwOt8sEMYTP","remoteAddr":"192.168.1.170","app":"PHP","message":"Unknown: POST Content-Length of 204 bytes exceeds the limit of 2 bytes at Unknown#0","level":3,"time":"2017-03-08T18:27:14+00:00","method":"POST","url":"\/index.php","user":"--"}
{"reqId":"wNcNCCTxfnbhoOcfYx6P","remoteAddr":"192.168.1.170","app":"PHP","message":"Automatically populating $HTTP_RAW_POST_DATA is deprecated and will be removed in a future version. To avoid this warning set 'always_populate_raw_post_data' to '-1' in php.ini and use the php:\/\/input stream instead. at Unknown#0","level":3,"time":"2017-03-08T18:42:18+00:00","method":"POST","url":"\/index.php\/heartbeat","user":"--"}

Hi,

your issue is caused by this:

which is a misconfiguration on your PHP environment having a too small / wrong configured post_max_size in your php.ini. Putting those info in your favorite search engine should give you additional information.