Fetch call freezes

问题:

I am using fetch to read data from a API:

async _getDcnDetail(dcnId) {

         return await fetch(API_URL+'get_dcndetail', {
            method: "POST",
            headers: {
                'Accept': 'application/json',
                'Content-Type': 'application/json',
                'Authorization':'Bearer '+ this.state.accessToken
            },                
            body: JSON.stringify({
                DcnId: dcnId
            })
        }).then(response => response.json());

    }

Then I call it:

async componentDidMount() {

   let response = await this._getDcnDetail(dcn.DcnId);
   console.log(response);

}

But it "waits" eternally, it is not resolving the promise.

As I understand fetch returns a promise which gets resolved by response.json(). I use "await" to wait the promise to be resolved, so not sure, what is wrong.