Notification after invoice state

app/Models/CostUnit.php

@@ -3,6 +3,7 @@
 namespace App\Models;
 
 use App\Scopes\InstancedModel;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
 use Illuminate\Database\Eloquent\Relations\BelongsToMany;
 use Illuminate\Database\Eloquent\Relations\HasMany;
 
@@ -42,4 +43,8 @@ class CostUnit extends InstancedModel
     public function invoices() : hasMany {
         return $this->hasMany(Invoice::class);
     }
+
+    public function tenant() : BelongsTo {
+        return $this->belongsTo(Tenant::class, 'tenant', 'slug');
+    }
 }