'str' object has no attribute 'META'

Django's serializers are only for serializing QuerySets, but you're passing it a dict. If you want to serialize a dict, perhaps you're looking for Python's built-in json module.

json_serializer.serialize is supposed to be used with a queryset. More info here.

You should be able to achieve the same with this:

import json
data = json.dumps({ 'participant_specific_donation' : info , 'participant_specific_milestone' : info1 })

Hope this helps.