I would like to take payments using SquareReaderSDK for a particular locationId. The business has 3 different location IDs. It seems currently it takes payments only on behalf of the Main locationId. One reason for this is to send the webhook to a different server. How can I tell the SquareReaderSDK that this payment belongs to a specific locationId programmatically.
With the Reader SDK when you generate the mobile authorization code you will be able to select the location ID that you would like the payments to go to. If you want to change locations you’ll need to deauthorize and reauthorize with the location you want the payments to go to. 
$mobileAuthorizationApi = $client->getMobileAuthorizationApi();
$body = new CreateMobileAuthorizationCodeRequest;
$body->setLocationId($locationId);
Ok. I found this. Good Answer Bryan. Thank you