In order to offer your application to existing Betfair customers, you need to distribute this under the terms of the Betfair Software Vendor License. You can find further details of the Vendor Program licensing process via https://developer.betfair.com/vendor-program/the-process/
There is a £499 license fee for Software Vendors which is payable once the application has been submitted for security certification. All applications are subject to our security and product requirements
To apply please complete the Software Vendor Application form.