We required to add external material in create Assignment in Schoology REST API but in documentation there are some basic fields only.
POST https://api.schoology.com/v1/sections/{section_id}/assignments
{ "title": "The assignment title", "description": "The assignment description", "due": "2014-09-25 11:30:00", "type": "assignment", "assignees":[ 12345, 4567], "grading_group_ids": [534], "count_in_grade": 0 }
How we can add external material using REST API of Schoology.