Days (Monday or Friday mandatory. Minimum 2 days)

Any assistance would be appreciated.
The client wants the following checkboxes:

Days (Monday or Friday mandatory. Minimum 2 days)
Monday Tuesday Wednesday Thursday Friday

Monday OR Friday are mandatory.

So, the visitor can select Monday, or Friday, or both Monday and Friday.

I just don’t know how to code this, as the variables are going to be peculiar and not logical?

But, the client has directed me to this page : https://oac.edu.au/our_campuses/join_waitlist where it is done. So, I know it’s possible.

Please help!

Thanks

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