Problem with USSD code *333*

I'm from Mauritania.

our operator Mauritel uses the USSD code * 333 * for the transfer of credit using the following query:

* 333 * MSISDN_of_destination * amount*transfert_code #

But whenever I type this query on my Iphone 4s, I get the following response:

Could you please help me to bypasse this problem.

Best regards