According to your first post, it looks like you defined DATE_INPUT_FORMATS in the localization file for it language. This is what django uses to parse input dates from form fields.
Here, you’re using Django Rest Framework which does not rely on such localization parameter. As stated in the documentation for such serializer field, the input formats are taken from the DATE_INPUT_FORMATS setting, which, in the context of DRF, means the “DATE_INPUT_FORMATS” entry of the REST_FRAMEWORK setting.