App: Extendon Plug-in error "hostname match not found" !

[Youthful-Wonder]

I have installed the Extendon app for the purpose of OTP login for my website. And according to the user guide provided. I have followed all the instructions and connected it to Firebase. 

However, the issue is that when I input my login number on the website, the error " Hostname match not found" pops out. (screenshot attached)

Would love to know how this can solved.