FR creation error

[2022-04-05 02:47:57,173] log: WARNING - Bad Request: /api/v2/create_field_report/
[2022-04-05 02:50:07,907] drf_views: ERROR - Could not create Field Report.
Traceback (most recent call last):
  File "/home/ifrc/go-api/api/drf_views.py", line 910, in create
    fieldreport = FieldReport.objects.create(**data)
  File "/usr/local/lib/python3.8/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/modeltranslation/manager.py", line 362, in create
    return super(MultilingualQuerySet, self).create(**kwargs)
  File "/usr/local/lib/python3.8/site-packages/django/db/models/query.py", line 422, in create
    obj.save(force_insert=True, using=self.db)
  File "/home/ifrc/go-api/api/models.py", line 1402, in save
    return super(FieldReport, self).save(*args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/django/db/models/base.py", line 743, in save
    self.save_base(using=using, force_insert=force_insert,
  File "/usr/local/lib/python3.8/site-packages/django/db/models/base.py", line 791, in save_base
    post_save.send(
  File "/usr/local/lib/python3.8/site-packages/django/dispatch/dispatcher.py", line 173, in send
    return [
  File "/usr/local/lib/python3.8/site-packages/django/dispatch/dispatcher.py", line 174, in <listcomp>
    (receiver, receiver(signal=self, sender=sender, **named))
  File "/usr/local/lib/python3.8/site-packages/reversion/revisions.py", line 328, in _post_save_receiver
    add_to_revision(instance, model_db=using)
  File "/usr/local/lib/python3.8/site-packages/reversion/revisions.py", line 213, in add_to_revision
    _add_to_revision(obj, db, model_db, True)
  File "/usr/local/lib/python3.8/site-packages/reversion/revisions.py", line 189, in _add_to_revision
    serialized_data=serializers.serialize(
  File "/usr/local/lib/python3.8/site-packages/django/core/serializers/__init__.py", line 128, in serialize
    s.serialize(queryset, **options)
  File "/usr/local/lib/python3.8/site-packages/django/core/serializers/base.py", line 107, in serialize
    self.handle_field(obj, field)
  File "/usr/local/lib/python3.8/site-packages/django/core/serializers/python.py", line 50, in handle_field
    self._current[field.name] = self._value_from_field(obj, field)
  File "/usr/local/lib/python3.8/site-packages/django/core/serializers/python.py", line 47, in _value_from_field
    return value if is_protected_type(value) else field.value_to_string(obj)
  File "/usr/local/lib/python3.8/site-packages/django/db/models/fields/__init__.py", line 1440, in value_to_string
    return '' if val is None else val.isoformat()
AttributeError: 'str' object has no attribute 'isoformat'