This plugin extends WooCommerce and provides a secure Iframe based checkout method using Westpac PayWay.

Noted That:

To install correctly this woo-westpac-payway-payment-gateway.zip.
Fisrt Download the woo-westpac-payway-payment-gateway.zip to your computer
Extract/Open woo-westpac-payway-payment-gateway.zip to Your Computer.
Then, Find readme.txt file inside woo-westpac-payway-payment-gateway.zip and Open readme.txt.
Now, Read the Requirements of this plugin. Which Wordpress Version and PHP Version are required to run this Plugin in Your Wordpress Site.
Then, Follow the the Tips Below.

Start the Tips:

1. First Download "woo-westpac-payway-payment-gateway.zip" Plugin to your Local Computer. (Click Download)

2. Then, Login to your "yourdomain.com/wp-admin" Dashboard.

3. Then, Click on "Plugins" + "Add New" from left sidemenu of Dashboard.

4. Now, Click on "Upload Plugin" button.

5. Now, Browse "woo-westpac-payway-payment-gateway.zip" Downloaded plugin from your computer, Where you downloaded woo-westpac-payway-payment-gateway.zip According to Step – 1 Above then, click on "Install Now"

6. Now, Click on "Active Plugin"

7. Then, See left sidemenu. "Westpac PayWay NET Payment Gateway for WooCommerce" folder is added on left sidemenu. Now, Click on "Westpac PayWay NET Payment Gateway for WooCommerce" folder.

Noted that: If you do not see "Westpac PayWay NET Payment Gateway for WooCommerce" folder on left sidemenu then, see at left sidemenu "Settings" or "Tools".

8. Now you configure yourself oR Watch video tutorial below about Westpac PayWay NET Payment Gateway for WooCommerce Configurtions and Settings or How to work "Westpac PayWay NET Payment Gateway for WooCommerce" in your WordPress site.

After Activated Plugin According to Step-6 then,

Go to "Plugins" + "Installed Plugin" from Wordpress Admin Panel Leftside Menu.
or Direct go to: https://yourdomain/wp-admin/plugins.php
Then, Find "Westpac PayWay NET Payment Gateway for WooCommerce" Activated Plugin from Plugin List.
Then, Click on "Settings" from Plugin that is Westpac PayWay NET Payment Gateway for WooCommerce
Now, Edit/Add/Config the setting and Click on "Save Changes" button,

Guide

Guide
Upload the plugin files to the `/wp-content/plugins/plugin-name` directory, or install the plugin through the WordPress plugins screen directly. Activate the plugin through the ‘Plugins’ screen in WordPress Use the Settings->Plugin Name screen to configure the plugin (Make your instructions match the desired user flow for activating and installing your plugin. Include any steps that might be needed for explanatory purposes)

Upload the plugin files to the /wp-content/plugins/plugin-name directory, or install the plugin through the WordPress plugins screen directly.
Activate the plugin through the ‘Plugins’ screen in WordPress
Use the Settings->Plugin Name screen to configure the plugin
(Make your instructions match the desired user flow for activating and installing your plugin. Include any steps that might be needed for explanatory purposes)

method, checkout, using, westpac, payway, based, iframe, extends, woocommerce, provides,

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Reffered: https://wordpress.org/