Recursive relationship with scope

A user has a sponsor:

public function sponsor()
{
    return $this->belongsTo(User::class, 'sponsor_id');
}

A user has referrals:

public function referrals()
{
    return $this->hasMany(User::class, 'sponsor_id');
}

A user is considered capped when they have 2 or more referrals:

public function activeReferrals()
{
    return $this->referrals()->whereActive(true);
}

public function isCapped()
{
    return $this->activeReferrals()->count() >= 2;
}

A user can give points. By default, the sponsor will receive them, but if the sponsor is capped, I want the points to go to a sponsor's referral that is NOT capped. If all the referrals are capped, then it does the same thing with the level below (the referral's referrals).

If I go user by user making database calls for each one, it's gonna take a long time. How can I write a scope that makes recursive calls until it finds the first active referral in the tree that's not capped?

This is what I'm trying to do: