Where you would add a link to a website rather than using http: use tel: followed by the full phone number, as the internet is international its a good idea to use the international version of the number.
Use https://wa.me/<number> where the <number> is a full phone number in international format. Drop any zeroes, brackets, or dashes when adding the phone number in international format.
First you need to get your invite link:
- Go to the WhatsApp group chat, then tap the group subject.
- Tap Invite via link.
- Choose Send link via WhatsApp, Copy link, Share link via another app, or QR code.
- You can now use the link like a link to a website.