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. See more about campaign payments here.