You can do this in the workspace using HTTPCallers. The first one will get the IDs and explode them into individual features - one for each ID. The features can then be passed to the second HTTPCaller where the ID attribute is used to form the request URL

​@hkingsbury I extracted ID data from the first HTTP caller and created a list named `project_task_id` that contains all the IDs. Next, I used the Attribute Creator to create an attribute called "url," appending the `project_task_id` field to the end of the URL. I then passed this "url" attribute to the second HTTP caller in the Request URL section, but the request failed.

Well you’re on the right track - most likely there is just something small you are missing. Check and double check your calls for typos. Hopefully the error you’re getting back from the API give you some hints as to what is going wrong. 

I’ve spent plenty of time banging my head against the wall with FME wondering why my API calls aren’t working only to notice my URL is off by a single letter or missing a key parameter required by the call.

It could be something as simple as having a / at the end or not. I once ran into an API that made a huge difference between the url having a / at the end or not, so I agree with Matt. Check the documentation for the API carefully, build a url that you know works using your data, then try to replicate that url in FME. Using your browser or Postman can be very helpful here.

The basic structure you have is correct: I have workspaces that have to chain multiple calls to REST API’s, and it works just fine (1 search for an adress, 2 get details of address, 3 get link to building info, 4th get the building polygon + info). It can definitely be achieved using FME.

Thank you all for the assistance! I was able to correct the URL, and it worked. It was indeed a very simple thing that I been overlooking.