No, using live account should be OK.
It seems that this is a bug with PowerStore. To fix this issue, change this line in your checkout.php file from:
$WA_PP_ECO_Set_params[1][$nextIndex] = "".($WAGLOBAL_Paypal_Sandbox == 1)?"true":"false" ."";
to
$WA_PP_ECO_Set_params[1][$nextIndex] = "false";
and then change this line on your pp_confirm.php file from:
$WA_PP_ECO_GetResult = WA_PP_ECO_Get_Post("".$WAGLOBAL_Paypal_User ."", "".$WAGLOBAL_Paypal_Password ."", "".$WAGLOBAL_Paypal_Signature ."", ($WAGLOBAL_Paypal_Sandbox == 1)?"true":"false". "");
to
$WA_PP_ECO_GetResult = WA_PP_ECO_Get_Post("".$WAGLOBAL_Paypal_User ."", "".$WAGLOBAL_Paypal_Password ."", "".$WAGLOBAL_Paypal_Signature ."false");
This will make sure that powerstore is always using the right url to post to.
