If you are using the offer_price pricing model, you can update the offer_price using this patch call. 

Request

PUT $apihost/$basepath/surveys/7654/offerPrice

($apihost is the environment against which you are testing, and $basepath is the base path with the api version. All Buy API calls will require access-token parameter in the header) 

Body: 

{
"value":1.45
}

Response

Response Code

200