Possible Unhandled Promise Rejection Type Error Undefined is not an object

I have this code in my React Native project:

static async validateSub(sub,pin) {

   sub_can_access = 'no'

   url = 'https://server.com/validator.php'

   let resp = await fetch(url + '?param1='+sub+'&param2='+pin);

   if (resp._bodyText.indexOf("TRUE") >= 0) {

       AsyncStorage.setItem('email', sub)
       AsyncStorage.setItem('password', pin)
       sub_can_access = 'yes'

    } else {

       alert('Try Again');

    }
}

The server returns the text TRUE Blah Blah Blah. And on Android it works fine, but for iOS, the variable resp comes undefined.

What could be happening?