I and many others did experience the same issue earlier this week, cause the system was overloaded but that was resolved, having the access code means your information has been registered. Suggest calling the phuket sandbox helpline to investigate.
this is a problem of their own making, they underestimated the sheer volume of requests and they're processing them which at times seems random eg requests for March arrival are being approved, whereas arrivals for next few days seem to be ignored unless you chase them up! Posters have been successfully approved via that email add..