title: Firebase Phone Auth: some users don't receive OTP
body: <p>I am facing a strange issue of some phone numbers do not receive OTP without receiving any errors, just nothing happens. Almost all the users are receiving the OTP just fine, except for only very few. How can I debug the issue? Does Firebase Auth have some log with any errors? Is my code missing something?</p>
  <p>Here is the code (in Flutter) for sending the OTP</p>
  <pre><code>sendOtp(String number, BuildContext context) async {
      print(&quot;Sending OTp&quot;);
      state = ViewState.Busy;
      await auth.verifyPhoneNumber(
        phoneNumber: '+966$number',
        timeout: Duration(seconds: 30),
        verificationCompleted: (AuthCredential credential) {
          print(&quot;Verified&quot;);
          signInWCredential(credential, context, number);
        },
        verificationFailed: (FirebaseAuthException e) {
          print(&quot;verification error code is: ${e.code}&quot;);
          print(&quot;verification error message is: ${e.message}&quot;);
          if (e.code == &quot;too-many-requests&quot;) {
            Dialogs.dialog(
                    context,
                    &quot;${Localization.of(context).error}!&quot;,
                    Localization.of(context).tooManyOtpRequestsError,
                    Localization.of(context).ok,
                    isDoublePop: true)
                .then((value) {
              if (value == ConfirmAction.ACCEPT) {
                Navigator.of(context).pop();
              }
            });
          } else {
            FirebaseCrashlytics.instance.recordError(e, StackTrace.current);
            print(&quot;Error is: $e&quot;);
            Dialogs.dialog(
                context,
                &quot;${Localization.of(context).error}!&quot;,
                Localization.of(context).errorSendingOtp,
                Localization.of(context).ok,
                isDoublePop: true);
          }
        },
        codeSent: (String verificationId, [int resendToken]) {
          print(&quot;Code sent&quot;);
          print(&quot;verification ID is: $verificationId&quot;);
          setVerificationId(verificationId);
          print(&quot;Resend token is: $resendToken&quot;);
          state = ViewState.Idle;
        },
        codeAutoRetrievalTimeout: (String verificationId) {},
      );
    }
  </code></pre>