- mongodb/mongodb 1.2.0 requires ext-mongodb ^1.3.0 -> the requested PHP extension mongodb is missing from your system

Composer is giving you the right answer there, you are using the wrong library.Don't use --ignore-platform-reqs, or you can, which to force install it.What you need to do now is check which library fits your php version. Write

php --version

if you don't know which one you are using. Output should be something like:

PHP 5.6.30-0+deb8u1 (cli) (built: Feb  8 2017 09:49:20)Copyright (c) 1997-2016 The PHP GroupZend Engine v2.6.0, Copyright (c) 1998-2016 Zend Technologies    with Zend OPcache v7.0.6-dev, Copyright (c) 1999-2016, by Zend Technologies

Find your version in the list below.

See the description in mongodb: PHP-Driver for mongodb

Head over to pecl and download whichever version fits your php version number.

in your case (PHP5.6):

$ wget https://pecl.php.net/get/mongodb-1.2.11.tgz$ tar -xvzf mongodb-1.2.11.tgz$ cd mongodb-1.2.11/$ phpize$ ./configure$ make all -j 5$ sudo make install

now it should work.

You can test the php mongodb connection with this code (finding an ObjectId) :

<?php# filename ConnectMongo.phprequire_once __DIR__ . "/vendor/autoload.php";ini_set('display_errors', 1);ini_set('display_startup_errors', 1);error_reporting(E_ALL);// connect to mongodb$manager = new MongoDB\Driver\Manager('mongodb://username:password@host');$id = new \MongoDB\BSON\ObjectId("5a0c8e2362eb6404c2f10032");$filter = ['_id' => $id];$options = [];$query = new \MongoDB\Driver\Query($filter, $options);$rows   = $manager->executeQuery('db.collection', $query);foreach ($rows as $document) {    var_dump($document);}?>

In terminal write this to test the connection:

$ php ConnectMongo.php

Make sure that you also install using composer, you should not get that same error anymore.

Run

pecl upgrade mongodb

If it complains about phpize, run

sudo apt install php7.x-dev

Replace 7.x with your PHP version. E.g. -

sudo apt install php7.3-dev

Try this

sudo apt-get install php-mongodb