I am trying to use Batch API to lock (or unlock) a group parts for a specified project. The batch portion does not work. Please help to check if I build the batch in a wrong way.

Reading parts from the project ( beginning and ending portions) works well.
I tried different ways in the batch portion with no luck. Got 500 “An unexpected server error has occurred”.

Here is my code:

importrequests
importjson
auth=('**************', '******************')
base='https://api.polydyne.com/v1'
project=109
lock=True

res=requests.get('{}/projects/{}/award_parts'.format(base, project), auth=auth)
parts=json.loads(res.text)
print('Before:')
forpartinparts:
    print('t', part['partId'], part['locked'])

batch= []
forpartinparts:
    req= {
            "method": 'PATCH',
            "resource": '/projects/{}/award_parts/{}'.format(project, part['partId']),
            "body": {
                "locked": lock
            }
          }
    batch.append(req)    

res=requests.post('{}/batch'.format(base), data=json.dumps(batch), auth=auth, headers={'Content-Type': 'application/json'})

res=requests.get('{}/projects/{}/award_parts'.format(base, project), auth=auth)
parts=json.loads(res.text)
print('After:')
forpartinparts:
    print('t', part['partId'], part['locked'])