I have created a testnet wallet on testnet.blockchain.info and added some testnet bitcoins to it.

I want to test the payment APIs so I am following the documentation on how to Generate a receive address. Yet I do not see a way or an URI to register a testnet receive address.

I tried to use it as is and I've put my testnet xpub in the query but I get this error:

{
    "message": "Invalid xpub format",
    "description": "Ensure you provide an xpub key, rather than an address"
}

Anyone had success using blockchain's payment APIs with testnet before?