[Is not a valid bitcoin address]

Hi people,

First of all, sorry for this principiant question.
It´s my first time using this modality.

Recently i downloaded the "Dark Wallet"

The program, generated an Steath code so that I can receive payments anonymously.

Situation:

My client have 3 bitcoins in his Coin.MX wallet.
When he tries to transfer this BTC to my wallet, using my Stealth Code, Coin.MX said "Is not a valid bitcoin address"

All of my clients, buy BTC using Credit Cards in coinbase or coin.mx
I need to solve this question...

What i´m doing wrong ?

Thanks !

John from Argentina