Magento 2 – Add Custom Payment Method to Configuration

If you have access to the DB of the site, take a look at the setup_module table to see if your module is showing up there. It should have the name and the current module version. If it's not showing up in that table, then your configuration files are incorrect. A module only requires two files to be registered:

app/code/{{vender_name}}/{{module_name}}/etc/module.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="{{vender_name}}_{{module_name}}" setup_version="0.0.1"/>
</config>

and

app/code/{{vender_name}}/{{module_name}}/registration.php

<?php
    \Magento\Framework\Component\ComponentRegistrar::register(
        \Magento\Framework\Component\ComponentRegistrar::MODULE,
        '{{vender_name}}_{{module_name}}',
        __DIR__
    );

If your module is registered correctly, then your next step is de-bugging the module's code. I would recommend looking at the layout xml files and the controller files that should be hitting, as this is the first step in any module's life cycle.

First, make sure apache “rewrite_module” is enable and then restart the server.

If this hasn't worked. Then do following steps:

1. Edit the file /etc/apache2/apache2.conf.
2. Find this code:

<Directory /var/www/>
        Options Indexes FollowSymLinks
        AllowOverride None
        Require all granted
</Directory>

3. Change "AllowOverride None" to "AllowOverride All".

<Directory /var/www/>
        Options Indexes FollowSymLinks
        AllowOverride All
        Require all granted 
</Directory>

4. Restart apache2.