Delegation from Auth0 to Firebase does not function - ios

Question

I have a firebase app. Authentication provider is Auth0, all my users are residing in auth0. I am trying to login with auth0 and than with delegation creating a jwt token to use in firebase. But from firebase I am getting an error.
The error is
Login Error happened: Optional(Error Domain=FIRAuthErrorDomain Code=17999 "An internal error has occurred, print and inspect the error details for more information." UserInfo={NSUnderlyingError=0x618000252ed0 {Error Domain=FIRAuthInternalErrorDomain Code=3 "(null)" UserInfo={FIRAuthErrorUserInfoDeserializedResponseKey={
code = 400;
errors = (
{
domain = usageLimits;
message = "Bad Request";
reason = keyExpired;
}
);
message = "Bad Request"; }}}, error_name=ERROR_INTERNAL_ERROR, NSLocalizedDescription=An internal error has occurred, print and inspect the error details for more information.})
However, the JWT is okay and the id_token is not expired. The payload is
{
"uid": "auth0|58f1d133c6623f69e82eaccd",
"iat": 1492376288,
"exp": 1492379888,
"aud": "https://identitytoolkit.googleapis.com/google.identity.identitytoolkit.v1.IdentityToolkit",
"iss": "firebase-adminsdk-b69t9#mein-dienstplan-6cd8e.iam.gserviceaccount.com",
"sub": "firebase-adminsdk-b69t9#mein-dienstplan-6cd8e.iam.gserviceaccount.com"
}
The code segment show, what I am doing after authenticating teh user with email/password and getting the id_token,
Auth0
.authentication()
.delegation(withParameters: ["id_token": self.id_token!,
"target_client": "116821977303633943003",
"grant_type" : "urn:ietf:params:oauth:grant-type:jwt-bearer",
"scope": "openid profile",
"api_type": "firebase"])
.start { result in
switch(result) {
case .success(let credentials):
if let idToken = credentials["id_token"] as? String {
print("FIREBASE TOKEN = \(idToken)")
FIRAuth.auth()?.signIn(withCustomToken: idToken) { (user, error) in
guard let user = user else {
callback(error)
return
}
print("Firebase user \(user)")
callback(nil)
}
callback(nil)
} else {
callback(UserSessionError.noIdToken)
}
case .failure(let error):
callback(error)
}
}
This code brings the error above.
Anyone has any idea what is wrong ? Thx in advance...