Create an API connection between 2 systems

Hi, I would to ask you to create an API connection between to applications. First application is called Kaseya BMS, this is my main application where i can create tickets and use time registration to keep track of my time spend. Further more i could close the ticket and then start a billing process. Because the billing process is time consuming i am looking for a connection to the second application which is called WeFact. What needs to be accomplished is that all my closed tickets are exported to WeFact which can create a example invoice. End result should be a way where i can select the tickets which are closed to being exported to WeFact. I need a choice to export selected tickets to WeFact. In WeFact there should be generated an example invoice wich has a line for each ticket title. The ticket title should be # ticket number - ticket title and the total time spent on that specific ticket. When the invoice is being send to the customer from WeFact, the invoice number should be put somewhere on the invoice in BMS so i got some reference. The API information for Kaseya BMS is available here: [login to view URL] The API information for WeFact is available here: [login to view URL] This is in dutch and i think you need to use Google Translate to translate the text around the code. I have seen a solution with other products which uses a middleware page to accomplish the above steps. If needed, that is not a problem.