Phone verification issue

[akashtw1]

I am running the demo authentication
My all other verification is working google oauth etc but not working phone verification

Error response
{
"error": {
"code": 400,
"message": "INVALID_APP_CREDENTIAL",
"errors": [
{
"message": "INVALID_APP_CREDENTIAL",
"domain": "global",
"reason": "invalid"
}
]
}
}
But when use a number which is added for testing purpose then there is no error
There is some error in firebase
I enabled the billing account and assigned it too