laravel relation ship

@shaungbhone I've already created my models, using oneToMany makes no sense, since a user will only hold one domain, but a domain can be associated to more users.

Domain:

public function users()
{
    return $this->hasManyThrough(
        User::class,
        UserDomain::class,
        'domain_id',
        'id',
        'id',
        'user_id'
    );
}

User:

public function domain()
{
    return $this->hasOneThrough(
        Domain::class,
        UserDomain::class,
        'user_id',
        'id',
        'id',
        'domain_id'
    );
}

But how can I create a new relation (UserDomain)?

    $domain = Domain::find(1);
    User::find(1)->domain()->create($domain);

already tried:

    $domain = Domain::find(1);
    User::find(1)->domain()->associate($domain);

None of this worked.