For most creators, legality is less of an issue than TikTok's own rules, which forbid fake engagement and the trade in it. TikTok removes fake accounts and the likes and follows they leave, and accounts involved can lose reach or features.
The law can matter too. In the United States, a Federal Trade Commission rule in force since 2024 bans buying or selling fake indicators of social media influence, such as bot followers or views, when they're used to misrepresent influence for commercial purposes. Rules differ by country, and this isn't legal advice.
Safety is the more immediate risk. Sites that want your TikTok login, or ask you to sign in with TikTok, are asking for access no growth service needs.