I got the same error too when I try to add new version to testfligh.
{
"errors" : [ {
"id" : "88a7b2d4-8285-46a1-850d-e0d43a8fd357",
"status" : "422",
"code" : "ENTITY_UNPROCESSABLE.BETA_CONTRACT_MISSING",
"title" : "Beta contract is missing for the app.",
"detail" : "Beta Contract is missing."
} ]
}