old_contents: from corehq.apps.domain.models import Domain
  from corehq.apps.sms.api import send_sms_to_verified_number
  
  def fallback_handler(v, text, msg):
      domain_obj = Domain.get_by_name(v.domain, strict=True)
      if domain_obj.use_default_sms_response and domain_obj.default_sms_response:
          send_sms_to_verified_number(v, domain_obj.default_sms_response)
      return True
  
  
new_contents: from corehq.apps.domain.models import Domain
  from corehq.apps.sms.api import (
      send_sms_to_verified_number,
      MessageMetadata,
      add_msg_tags,
  )
  from corehq.apps.sms.models import WORKFLOW_DEFAULT
  
  
  def fallback_handler(v, text, msg):
      domain_obj = Domain.get_by_name(v.domain, strict=True)
      default_workflow_meta = MessageMetadata(workflow=WORKFLOW_DEFAULT)
      if domain_obj.use_default_sms_response and domain_obj.default_sms_response:
          send_sms_to_verified_number(v, domain_obj.default_sms_response,
                                      metadata=default_workflow_meta)
      else:
          add_msg_tags(msg, default_workflow_meta)
      return True
  
  
subject: handle adding WORKFLOW_DEFAULT tag to messages for the fallback handler