A prevet is simply a request on behalf of an advertiser to see if you are interested in working with a brand. It is not yet a campaign request, and there are no commercial terms associated with a prevet. Sometimes, advertisers will ask specific questions related to the prospective campaign that you will be required to answer.
A campaign is a specific request on behalf of the advertiser for you to participate. You will be able to see a summary of the campaign’s expectations and commercial terms. If you accept the request, you are legally bound by the terms and requirements of the campaign.