PHP / FCM : double notification & click not working - php

Question

I'm using PHP to send browser notifications through cURL (with Firebase) and while notifications are sent to their destination (desktop and mobile browsers), I'm facing two problems:
Each time I send a notification, I get two notifications in the browser. One with the content I have defined (see below) and one empty but considered as a background notification. I think it has something to do with active window but I don't know how to go around this.
When I click on the notification I have received, the link is never working.
I use the following code to send the notification:
$msg = urlencode($message);
$
$data = array(
'title'=>"My title",
'sound' => "default",
'msg'=>"my message",
'data'=>$datapayload,
'body'=>"message",
'color' => "#FF33CC",
'link' => "mylink"
);
if($img)
{
$data["image"] = "xxx";
$data["style"] = "picture";
$data["picture"] = "xxx";
}
$fields = array(
'to'=>$to,
'notification'=>$data,
"priority" => "high",
"link"=>"mylink",
"data"=>$data
);
$headers = array(
'Authorization: key=xxxx',
'Content-Type: application/json'
);
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, 'https://fcm.googleapis.com/fcm/send');
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
$result = curl_exec($ch);
curl_close( $ch );
When I send notifications with this script, I get the following output from the cURL request:
{"multicast_id":xxx,"success":1,"failure":0,"canonical_ids":0,"results":[{"message_id":"xxx"}]}
And here is an example of the JSON send to FCM:
Array
(
[to] => xxx
[notification] => Array
(
[title] => Notification pour Chrome Samsung
[sound] => default
[msg] => blablabla
[data] => Array
(
[ID] => xxxx
)
[body] => blablabla
[color] => #FF33CC
[link] => https://www.something.com
[image] => https://www.something.com/logo.png
[style] => picture
[picture] => https://www.something.com/logo.png
)
[priority] => high
[link] => https://www.something.com
[data] => Array
(
[title] => blabla
[sound] => default
[msg] => blablabla
[data] => Array
(
[ID] => 653804269445
)
[body] => blablabla
[color] => #FF33CC
[link] => https://www.something.com
[image] => https://www.something.com/logo.png
[style] => picture
[picture] => https://www.something.com/logo.png
)
)
I have tried to use only data or only notification but I still end up with 2 non clickable messages. I saw "click_action" in the documentation but it looks like it was only to be used for Android devices.
Any idea?
Thanks!
Update: the generic messages I get in the notification are obviously coming from the service worker but no matter what I do, updating the service worker doesn't seem to change anything.