That's a good question! I understand you want to invite your students to your What's App Group. You are welcome to share your contact information or other services in the bonus lecture of your course.
There are a few things you have to consider when adding the bonus lecture, for example:
Please click here to learn more about the rules and guidelines.
If you have additional questions about the bonus lecture, please reach out to the policy team at firstname.lastname@example.org.
I hope this helps and I wish you a great week!