WHMCS Invoice payment using SOAP Web Services

I am looking for a freelancer to integrate a cash/POS payment option with our WHMCS system. POS pay points already exists and will simply be integrating into our existing environment. The ideal candidate should have experience in integrating payment gateways with WHMCS and knowledge of POS systems. They should also be able to provide solutions for any potential issues that may arise during the integration process. The payment options we are considering are Netcash, Kazang and Flash. We intend on starting with Netcash as they are in most retail environments and extend to the others. Integration steps are -: 1. Embed POS payment details (including barcodes) on each invoice printed in our environment, regardless of payment gateway. 2. Mark invoice as paid when payment for the invoice is reported as received either realtime or batch. 3. Real-time and cron based reconciliation will update invoice statuses. The coder should be able to work with multiple partners as payment methods for multiple partners may be printed on a single invoice. The coder should have their own WHMCS environment and be highly knowledgable in payments and WHMCS. Testing and bug fixing until project is 100% operational is essential. All small details missed in the description shouldn't constitute scope / price change. NB: THE CODER SHOULD KNOW HOW TO WORK WITH SOAP based Web services as well as Other APIs.