Error on aunthentication for phone otp : Error 503 & Error 39

[Linnister Cloud]

I am trying to use firebase aunthetiation for phone otp on  wordpress website but the i am getting an error below.

{\"code\":503,\"message\":\"Error code: 39\",\"errors\":[{\"message\":\"Error code: 39\",\"domain\":\"global\",\"reason\":\"backendError\"}]}}"}}}

I have tested with optional phone number and everything seems to work. But when I try to use a real mobile number then the error comes up.