Lottery on wordpress using php and json - php

Question

I am currently building a website for my guild (on a video game).
The video game (Guild wars 2) provide us a feed of everything being done inside the guild in a json file (user joining, withdraw of money, deposit of items, kick, etc...).
Since I have this feed, auto-updated, I would like to setup a lottery, working on the following :
- guild member (user) buy a ticket => deposit golds in our bank (displayed as deposit)
- display this information on the website => user "x" has bought a ticket at H:M:DD:MM:Y (for example)
- at the end of the month, script to random a winner from this list of users (this random must include only tickets bought between date A & B)
I have managed to write a little code, and it is working, only to display a list of users and their actions :
<?php
$apikey = '(My API key)';
$guildkey = '(My guild key)';
$jsontest =file_get_contents ('https://api.guildwars2.com/v2/guild/'.$guildkey.'/log?access_token='. $apikey);
$json = json_decode($jsontest,true);
foreach($json as $member)
{
if ($member['coins'] > 1)
print "Guild member "."".$member['user'].""." has bought a ticket for ".$member['coins']." golds"." ";
}
?>
Here a little example of how the guild wars 2 api output is :
{
"type": "upgrade",
"item_id": 77729,
"count": 1,
"action": "completed",
"id": 896815,
"time": "2017-02-23T14:26:29.000Z",
"user": "Lehi.5091",
"upgrade_id": 668
},
{
"id": 896814,
"time": "2017-02-23T14:26:29.000Z",
"type": "upgrade",
"upgrade_id": 668,
"action": "queued"
},
{
"type": "upgrade",
"item_id": 77729,
"count": 1,
"action": "completed",
"id": 896810,
"time": "2017-02-23T14:26:28.000Z",
"user": "Lehi.5091",
"upgrade_id": 668
As intended, it does display what I want, here the working code
If you have tips or anything about how to this, I'll gladly take them.
Thanks for your help,