[Django]-POSTing foreign keys to Django Rest Framework, using Postman

You need to change get_parameter method to get_parameter_name for example, and use two separate fields for parameter and parameter_name.

class DataCreateSerializer(ModelSerializer):
    sensor = SerializerMethodField()
    parameter_name = SerializerMethodField()
    class Meta:
        model = Data
        fields = [
            'id',
            'time',
            'sensor',
            'parameter', # it is the field for FK model field
            'parameter_name' # field for custom method
            'parameter_value'
        ]

    def get_sensor(self, obj):
        return str(obj.sensor)

    def get_parameter_name(self, obj):
        return str(obj.parameter.parameter_name)