A 'free' online TEFL course is used to collect your details and sign you up to a job board. The certification may not be recognised where it matters, leaving you paying again for a qualification that counts.
Check whether the certificate is accepted by the employers and visa authorities you actually need it for. Look for who promotes it — brand-new accounts pushing the same course is a warning sign.
A community moderator writing about promotion patterns they observed on their own subreddit, not a first-person employment account — the weakest evidence class in this file.