code: def get_token_identifiers(
          chain_state: ChainState,
          payment_network_id: PaymentNetworkID,
  ) -> List[TokenAddress]:
      
      payment_network = chain_state.identifiers_to_paymentnetworks.get(payment_network_id)
  
      if payment_network is not None:
          return [
              token_address
              for token_address in payment_network.tokenaddresses_to_tokenidentifiers.keys()
          ]
  
      return list()
docs: Return the list of tokens registered with the given payment network.