Hi Seolife ,
Thanks for sharing the link!
I took a look at your buttons and it looks like the WhatsApp button is correctly not adding the
+ symbol on your number.
The one that you had on your screenshot is the Call button that opens the phone app.
WhatsApp's share page adds the plus symbol themselves to make it work.
You mentioned that you are getting the "Looks like you don't have WhatsApp installed!" message when you try to click on the continue button on the WhatsApp page.
I was able to reproduce this issue on my android phone and the cause of it seems to be because I had the option. "Open links in apps" disabled in my browser settings and once enabling this again, WhatsApp was able to open the app for me.
Could you maybe try another browser and see if it will work and if it doesn't could you maybe let us know which browser are you testing this on?
Let me know! 😄