Adobe sign Setting expiry date problem

Dear Support team,

We are planning to use adobe sign & one small problem with continuing POC.

  I am getting below error while setting expiry date.

I use API to generate the agreements and the API documentation says: "PUT /agreements/{agreementId}

But if I want to change the expiration date on an existing and sent agreement, I get a message: "403 CANNOT_EDIT_AGREEMENT_EXPIRATION You do not have permission to set the expiration date for this agreement." But I use integration key with all permissions allowed.

Can't I change the expiration date.

Please help me asap

Following is the SDK code I use

            string client_id = "CBJCHBCAABAAS3nYEeZmkcFxyOxJdR7wyWsHGDyOAKkN";

            string client_secret = "XXXXXXXXXXXXXXX";

            ApiClient apiClient = new ApiClient(client_id, client_secret);

            apiClient.SetAccessToken(TempData["token"].ToString(), Session["refresh_token"].ToString(),DateTime.Now.AddSeconds(3600), api_access_point);

            AgreementsApi ap = new AgreementsApi(apiClient);

            AgreementInfo aii = ap.GetAgreementInfo(agreementId);

            aii.ExpirationTime = Convert.ToDateTime(DateTime.Now.ToUniversalTime().AddDays(7).ToString("yyyy-MM-ddTHH\\:mm\\:ssZ"));

       ap.UpdateAgreement(agreementId, aii);

I am getting "403 CANNOT_EDIT_AGREEMENT_EXPIRATION You do not have permission to set the expiration date for this agreement." But I use integration key with all permissions allowed.