You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: manifests.go
    path of file: ./repos/slack
    
    the code of the file until where you have to start completion: package slack

import (
	"context"
	"encoding/json"
	"net/url"
)

// Manifest is an application manifest schema
type Manifest struct {
	Metadata    ManifestMetadata `json:"_metadata,omitempty" yaml:"_metadata,omitempty"`
	Display     Display          `json:"display_information" yaml:"display_information"`
	Settings    Settings         `json:"settings,omitempty" yaml:"settings,omitempty"`
	Features    Features         `json:"features,omitempty" yaml:"features,omitempty"
    
func (api *Client) ValidateManifestContext(ctx context.Context, manifest *Manifest, token string, appId string) (*ManifestResponse, error) {
	if token == "" {
		token = api.configToken
	}

	// Marshal manifest into string
	jsonBytes, err := json.Marshal(manifest)
	if err != nil {
		return nil, err
	}

	values := url.Values{
		"token":    {token},
		"manifest": {string(jsonBytes)},
	}

	if appId != "" {
		values.Add("app_id", appId)
	}

	response := &ManifestResponse{}
	err = api.postMethod(ctx, "apps.manifest.validate", values, response)
	if err != nil {
		return nil, err
	}

	return response, response.Err()
}