Cannot search task with type "MULTI_INSTANCE_ACTIVITY"

I am making a staff-survey diagram with Parallel Multi-instatiation type task and timer to auto-create multiple tasks assigned to all staffs in my office.

The diagram has an overview page that will display list of staffs that submit their assigned task, and a summary container that will be hidden until all staffs have submited their tasks.

As I use the API "../API/bpm/task?p=0&c=9999&f=caseId={{caseId}}" to check the list of tasks, I saw that there will always be a task with type "MULTI_INSTANCE_ACTIVITY" when there is at least 1 staff not submit his/her assigned task. If all staffs submit the assigned tasks, this "MULTI_INSTANCE_ACTIVITY" task will auto-complete and no longer list.

Therefore, I intent to use the API "../API/bpm/task?p=0&c=9999&f=caseId={{caseId}}&f=type=MULTI_INSTANCE_ACTIVITY" to check if this task is there or not, and use this as a check to hidden or show the summary container.

However, the above API return error:

Can't convert < MULTI_INSTANCE_ACTIVITY >. Unknown flow node type.

If I change the type in the API to "USER_TASK", there is no error.

Why am I not be able to search with type=MULTI_INSTANCE_ACTIVITY?