Sync another Model - laravel-5.5

Question

I have a view for a location. This location, that has different services. They are both linked as has many in the model (n-m relation) in the model LocationService.
In this view, it is possible to select different tags for each service of the location. I have a model called location_service_tag, that has the id of the location_service and the id of the tags.
Now I want to store the tags of the location_service combination using the sync method. How is it possible to store this information?
Here is an example (The IDs are free chosen):
I have the view with the location 1.
This location has 2 services with the id 11, 22.
They are stored in location_service with the ids 111,122.
The location_service 111 has the tag id 1111, 2222, the location_service 122 has the tags 2222,4444.
Now I want to store these tags into location_service_tag using sync. How is this possible?
I thought it might be possible somehow like this, but it is not.
foreach($request->servicetags as $servicetag){
if(count($servicetag)>0){
//Final statement must be true, because we want to override e.g. if one is deleted or inserted
$location->locationservice()->tags()->sync($servicetag, true);
}else{
//There are no services, submit an empty array
$location->locationservice()->tags()->sync([], true);
}
}

Answer 1

Finally I did it with:
//Save relational Data of services
//If there are services, add the, else add empty array
if(isset($request->locationservices)){
foreach($request->locationservices as $key => $locationservice){
if(count($locationservice)>0){
LocationService::find($key)->tags()->sync($locationservice, true);
}else{
LocationService::find($key)->tags()->sync([], true);
}
}
}
The key has the locationservice_id as key and the value of the loop has the selected tag_ids as an array for each locationservice.