1. Login to FastSpring, if no account then create account first and create store and make sure it is Active/Approved.
2. Head on FastSpring Account to "Notification Section"
   
   
   
3. Edit Default Settings and Make sure box options below are ticket, and fill in your "Primary Account Contact" and "Store Notification Addresses" then save.
   
   
    Enable Default Order Email
    Enable Default Return Email
    
4.  Under Custom Notifications, click Add, type "Order Complete" and set To URL, with live server url:
   
   https://yourwhmcs.com/modules/gateways/callback/fastspring.php
   
    Replace "yourwhmcs.com" in url above with your WHMCS domain then press Next, fill the pages as seen below:
   
   
5. On Security Tab, note down the Private Key, this will be needed later on in WHMCS setup.
6. On HTTP Parameter tab make sure following fields exits if not then add them with the values as shown in screenshot below:
   
   OrderReferrer
   Status
   OrderID
   OrderSubTotalUSD
   Tax
   security_data
   security_hash
   

1. Click Save and set to Active.
   
   

WHMCS Installation and Activation:

1. Upload The Content of Module to WHMCS folder.
   
2. Head to WHMCS Admin area > Setup > Payment > Payments Gateways, From Activate module Dropdown select "FastSpring", and set:
   
   Display name: Fill a name of your liking like "Paypal and Credit card" 
   License code: Insert your Module License purchased from ModuleFactory
   FastSpring Private Key Security: Enter the Key we got from step 5 above in "FastSpring Integration Configuration" section.
   Test mode: you can tick this for testing mode, allow you to complete purchase on fastspring to test the full functionality without real pay
3. Click "Save Change"
   
   
   

1. Since Both are stores, so you need to create the products on both WHMCS and Fastspring.
2. Mapping happens by Product names, product names on fastspring and whmcs need to be identifcal.
3. For Coupons need to have same name on both systems as well to work.
   
   

Limitations:

1. Refund not supported yet.
2. Subscription not supported yet.
3. Custom invoices not supported yet, at the moment you need to manual create the invoice on both systems and in reference on fastspring invoice add the id of whmcs invoice for auto pay to reflect on it.