App id must be in a format of "com.yourdomain.appname" for example "com.instavr.yourappname"
App id must be created in three parts separated with two dots only.
You can check if your entered App Id is correct or not from App Id field border's color.
If App Id field border shows red color like below then your App Id is invalid.
If App Id field border shows green color like below then your App Id is valid.