Diagram

Flow explained:

1. A Contributor creates an order in the wallet front-end.

2. Contributor submits KYC and is verified.

3. Disposable Invoice address is created and displayed in the wallet front-end and sent via e-mail.

4. The Contributor sends BTC from his BTC wallet to Invoice Address.

5. Transaction is mined (fee is paid by the Contributor).

6. Keyserver monitors invoice address, and when the transaction is mined, it does 2 actions: 

    a) sends tokens to the Contributor's address;
    b) transfers BTC from the Invoice address to the Client's address.

7. Transaction is mined (fee is paid by the Client).

8. The final step:

    a) tokens are delivered to the Contributor's address. The Contributor is notified via e-mail;
    b) BTC is delivered to the Client's address.