listChannels 
  Lists all Channels created under a single Chime App as a paginated list. You can specify filters to narrow results.
Functionality & restrictions
- Use privacy = - PUBLICto retrieve all public channels in the account.
- Only an - AppInstanceAdmincan set privacy =- PRIVATEto list the private channels in an account.
The x-amz-chime-bearer request header is mandatory. Use the ARN of the AppInstanceUser or AppInstanceBot that makes the API call as the value in the header.