Using "getdatasubsetdownloadlinkfromprocess()" to export excel, the process is not triggering.

I haven't personally worked with this plugin before, but have you found anything within the documentation?

Also, a few notes:

1. How many rows of data are you dealing with? If there is too much data, the process will timeout for sure.

2. From what I've heard, if you are using downloaddatasubset link and you want filtered data to be exported then you will have to pass the applied filters to input named process variable as process parameter and write logic to apply filters in the process model as well. 

3. The cloud version uses the getdatasubsetdownloadlinkfromprocess() and the on-premise version uses getdatasubsetdownloadlinkfromrule(). Are you using the right version?

Further reference: https://docs.appian.com/suite/help/18.3/Export_To_Excel_Smart_Service.html and https://docs.appian.com/suite/help/18.3/Export_Multiple_DSEs_to_Excel.html 

While Prateek's reply is a considerable solution for your problem, I suggest you to be mindful while using a!startProcess, especially in this case.

1. When you use a!startProcess to start a process, the fv!processinfo fetches only that data , you get immediately after the process initiates and it would not wait till the process is complete. In order to fetch all the data, you need to activity-chain all the nodes or in this case, till you get the document id. Consider activity chaining all the nodes in the process , only if this process is critical or if it takes less than 5 seconds to execute, as it has adverse effects on the performance.

2. And I suggest instead of sending the datasubset in process parameters, consider using a stored procedure to get the relevant data inside the process created from the above approach.

Please configure your process model assignment as All nodes in this lane will run as an automated activity.