Outlook Add-in Can not get access token

[merhaba_merhaba]

Hi. I am trying to develop an outlook add-in and in my adding I want to forward and/or delete an email. for this I am using Microsoft exchange API like this

await axios.delete(`${OFFICE_URL}/me/messages/${mailId}`, {
      headers: {
        'Authorization': 'Bearer ' + accessToken,
        'Content-Type': 'application/json',
        'Accept': 'application/json',
      }
    });

 but to be able to this I need to get an access token. From the Microsoft documentation (Microsoft getCallbackTokenAsync) I am trying to get my access token like this.

async function getAccessToken() {
        return await new Promise((resolve, reject) => {
          Office.context.mailbox.getCallbackTokenAsync(
              { isRest: true },
              function (result) {
                if (result.status === Office.AsyncResultStatus.Succeeded) {
                  resolve(result.value);
                }
                else {
                  reject(new Error(result))
                }
              })
        });
      }

This code is not working approximately for a week but before it was working and I was not getting an error. But this is not the case anymore.  From developer tools, this is the request and payload I am sending.

requestpayload

Even though server responds with 200 (OK) it is not giving me my token. This is the response.

{
    "Header": {
        "ServerVersionInfo": {
            "MajorVersion": 15,
            "MinorVersion": 20,
            "MajorBuildNumber": 7292,
            "MinorBuildNumber": 29,
            "Version": "V2018_01_08"
        }
    },
    "Body": {
        "ResponseMessages": {
            "Items": [
                {
                    "__type": "GetClientAccessTokenResponseMessage:#Exchange",
                    "Token": null,
                    "MessageText": "An internal server error occurred. The operation failed., One or more errors occurred.",
                    "ResponseCode": "ErrorInternalServerError",
                    "ResponseClass": "Error"
                }
            ]
        }
    }
}

What I do not understand is that this was working fine just a week before and not just one time but it was working fine for more than a month.