Currently via the API, there is no way to tell Click and Drop which shipping method you intend for the order to be shipped. You are only able to setup rules based on price.

The 'Store Postage Method' is only currently able to be used for integrations which Royal Mail themselves have written. This is a strange practice and makes the API only half feasible.

Please add this or another new parameter so we can specify our postage method by name rather than price.