Hi Gemma!
Happy to help with this!
Reach 360 learners would first need to be enrolled before having access to training material. Even though Automatic Enrollment is a feature in Reach 360, you may want to explore other options such as Review 360. After publishing your lesson to Review 360, open your course in the Review 360 dashboard and share that URL with your external colleagues.
It's helpful to keep in mind that Review 360 is not a tracking tool. It is a collaboration tool for collecting feedback from stakeholders. If you require a way to track that agencies have taken a course, then Reach 360 would be the better fit.
Please let me know if you have any more questions!