Integartion and web Api

What this(APP_getTaskIdFromProcess) rule and fv!processInfo  is returning?

yes , process task report 

I have a hard time following your explanation. And it seems way too overcomplicated.

You can link to a task from any UI in Appian, across applications. The only thing you need is the task ID. Then, instead of trying to start another process that somehow displays that already existing task, just use a!processTaskLink to open it.

https://docs.appian.com/suite/help/24.1/Process_Task_Link_Component.html

thanks Stefan for your response but the main problem is user need's to start the process then it will generate the task id and that task id i can use in  processTaskLink , is there any way that user can start the process from different application and user input task get assign to him .

I am not sure what you mean. It is the nature of a user input task to be assigned to people. A use can start a process from anywhere and get that task assigned.

BTW, I suggest to make that initial user input task the start form of that process and load any required data inside the form. Then, your user would immediately see that start form.