src/Taggable.php
protected function addOneTag(string $tagName): void
    {
        /** @var Tag $tag */
        $tag = app(TagService::class)->findOrCreate($tagName);
        $tagKey = $tag->getKey();

        if (!$this->getAttribute('tags')->contains($tagKey)) {
            $this->tags()->attach($tagKey);
        }
    }
protected function addOneTag(string $tagName): void
    {
        /** @var Tag $tag */
        $tag = app(TagService::class)->findOrCreate($tagName);
        $tagKey = $tag->getKey();

        if (!$this->getAttribute('tags')->contains($tagKey)) {
            $this->tags()->attach($tagKey);
        }
    }
Add one tag to the model.

@param string $tagName