Courses on discourse are basically free to watch, with only some features requiring payment to use. For example, in the course Artificial Intelligence for Medical Diagnosis, assignments involving notebooks likely require payment (either purchasing the course or subscribing to discourse plus) due to cost considerations.
The good news is that I found my account can invite others. You can click here to pay 1 dollar for one month of Coursera Plus, during which all courses and all features will be fully accessible.