Not able to receive notifications in all devices

For my game, I have established notification system via custom server usage. So web developer created notification setup for me. In this, I am facing one problem. In my two iPhones, I am getting notification always but my client can't able to detect any notification in his any iPhone devices.

Whether it is problem of region?? Because I am in Asian region and my client belongs to Europe region. Right now we are in Sandbox environment.

Please give some suggestion in this because my project get stuck because only this reason.

EDIT: If I clearly set deviceToken of my iPhone in PHP code then I am getting notification but If I clearly set deviceToken of client iPhone then no notification deliver to him.

As well in PHP code, We were getting success for all deviceTokens, even client deviceTokens too, so we became too ambiguous now for what to do next!!!