Check the possibility of creating a proposal

Retrieves the result on the availability of creating a proposal via API based on user’s permissions and a combination of the input values: subscriberId + providerId + locationId + tradeId + currency. When the combination of the input values does not allow creating a proposal using API, the method returns the following response: “Proposal form is not supported via API. Please use the UI instead.” <br /> Having received the successful response, copy the response model from this method to use it as a request model in the POST proposals/Create proposal method. <br /> Note: Custom proposal forms are not supported.