The current official terms, in writing, from the government's own programme materials: the fee per person, the gift amount, who may be included as accompanying family, the classification the case proceeds under, and the payment mechanism. Nothing should be paid on the strength of an intermediary's description.
Verify against the source, not against a summary
The unusual feature of this route is that the first payment is made before any adjudication, which puts an ordinary consumer risk in front of the legal one. Three checks are worth completing first. Confirm the amounts and the structure on the official government page rather than in a brochure, a news article or an adviser's slide deck, because reported figures have drifted from published ones.
Confirm the payment channel is the official one, since a programme involving large transfers attracts imitation, and money sent to the wrong place is not recoverable. Confirm in writing which family members may accompany and on what terms, as that determines the total rather than the headline number. Alongside those, ordinary immigration documentation still applies: passports, civil documents, police and medical clearances, and full disclosure of prior immigration history.