Apollo + Angular mutation is not working with variables

I'm having troubles creating mutations with variables. I can make it work including the values directly, like this:

export const orderCancellation = gql`
mutation{
  cancelOrder(input: {id: 2649,  cancellationReasonId: 1 } ) {
    order{
      id,
      isCancelled
    }
  }
}`;

But when try to use variables nothing works:

export const orderCancellation = gql`
mutation cancelOrder($id: ID!, $cancellationReasonId: ID!) {
  cancelOrder(input: {id: $id,  cancellationReasonId: $cancellationReasonId }) {
    order {
      id,
      isCancelled
    }
  }
}`;

The custom error message from our server:

Didn't find any result for  'CancelOrderPayload' with the arguments '{:input=>#<#<Class:0x00005608dca67e90>:0x00005608e10cd790 @context=#<Query::Context ...>, @ruby_style_hash={:id=>nil, :cancellation_reason_id=>nil}, @arguments=#<GraphQL::Execution::Interpreter::Arguments @keyword_arguments={:id=>nil, :cancellation_reason_id=>nil}>, @maybe_lazies=[]>}.

And this is how I call the mutation:

this.apollo.mutate({
  mutation: orderCancellation,
  variables: {id: orderId, cancellationReasonId: reasonId}
});

Does any one has clue on what i'm doing wrong? Maybe it's a server side problem?

EDIT 1: Here is the request payload with variables implementation (took from Network tab on Chrome DevTools):

operationName: "cancelOrder"
query: "mutation cancelOrder($id: ID!, $cancellationReasonId: ID!) {↵  cancelOrder(input: {id: $id, cancellationReasonId: $cancellationReasonId}) {↵    order {↵      id↵      isCancelled↵      __typename↵    }↵    __typename↵  }↵}↵"
variables: {id: "3045", cancellationReasonId: "1"}

EDIT 2: Already tried to declare the mutation like this:

export const orderCancellation = gql`
mutation cancelOrder($input: CancelOrderInput!) {
  cancelOrder(input: $input) {
    order {
      id,
      isCancelled
    }
  }
}`;

this.apollo.mutate({
     mutation: orderCancellation,
     variables: {input: {id: orderId, cancellationReasonId: reasonId}}
  });