Browser-Based Merchant Payment Authorization Question

http://developer.mintchipchallenge.com/api/hosted/process.html

"If the user confirms the payment, the Remote MintChip Server creates the value-message and redirects the browser to the merchant URL encoded in the request-packet"

QUESTION: how do we encode the merchant URL using this Hosted API method:

http://developer.mintchipchallenge.com/api/hosted/CreateValueMessage.html

Create Value Message Without Annotation

POST /mintchip/payments/{payeeid}/{currencycode}/{amountincents}

Thank you,
Adrian