Firebase Dynamic link API returning unexpected res

问题:

I'm using Firebase API to generate short link:

https://firebasedynamiclinks.googleapis.com/v1/shortLinks?key=XYZ

It work most of time and generated expected result like https:// abc123.app.goo.gl/WXYZ but randomly it sometime generated https:// goo.gl/xyz sort of link. And finally when this executed by client it does not contain expected parsed result.

I have no idea why this is happening. Any one suggestion what's wrong going here.