Getting bad request response error in Tumblr api /posts endpoint

Question

I am using python for making a post request on tumblr /posts endpoint but getting an error response. This is the code. Tumblr api use oauth1 authentication.

import requests
from requests_oauthlib import OAuth1

consumer_key = "0000000000000000000000000000000000000"
consumer_secret = "0000000000000000000000000000000000000"
token = "0000000000000000000000000000000000000"
token_secret = "0000000000000000000000000000000000000"

oauth = OAuth1(
    consumer_key,
    client_secret=consumer_secret,
    resource_owner_key=token,
    resource_owner_secret=token_secret,
    signature_method='HMAC-SHA1'
)

url = 'https://api.tumblr.com/v2/blog/aisamarsha-blog.tumblr.com/posts'

params = {
    'type': 'photo',
    'state': 'published',
    'tags': 'tag1, tag2, tag3',
    'content': [
        {
            'type': 'image',
            'url': 'http://69.media.tumblr.com/b06fe71cc4ab47e93749df060ff54a90/tumblr_nshp8oVOnV1rg0s9xo1_250.jpg',
            'caption': 'This is the caption for image1'
        },
        {
            'type': 'image',
            'url': 'http://69.media.tumblr.com/b06fe71cc4ab47e93749df060ff54a90/tumblr_nshp8oVOnV1rg0s9xo1_250.jpg',
            'caption': 'This is the caption for image2'
        },
        {
            'type': 'image',
            'url': 'http://69.media.tumblr.com/b06fe71cc4ab47e93749df060ff54a90/tumblr_nshp8oVOnV1rg0s9xo1_1280.jpg',
            'caption': 'This is the caption for image3'
        }
    ]
}

response = requests.post(url, auth=oauth, json=params)

print(response.json())

I want to post blog with multple images, tags and caption on tumblr.