Adding Backend Post features to iPay88 payment gateway in Jomres

I'd a hotel reservation website built using Jomres. Previously I'd hired a developer to help me add iPay88 payment module to it. But afterward we found out the system was incomplete which is lack of Backend Post function, which caused many transaction lost, but the developer doesn't seem to be interest in fixing/completing the project eventhough we willing to pay him extra. So would need someone's help to add in the backend post function to the existing ipay88 module. Here i attached the API given by iPay88. It is quite urgent. Thanks very much in advance for anyone who is willing to help.