AttributeError: 'dict' object has no attribute 'split'

[PythonCoderAS]

When I try to run a simple test to log in to this API, I get an AttributeError:

_____________________________________________________________________________________________________________ test_login ______________________________________________________________________________________________________________

username = '<censored>', password = '<censored>'

    @pytest.mark.asyncio
    @pytest.mark.vcr()
    async def test_login(username, password):
        async with MangadexClient(username=username, password=password) as client:
>           await client.login()

tests/test_client.py:118: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
asyncdex/client.py:412: in login
    r = await self.request(
asyncdex/client.py:273: in request
    resp = await self.session.request(method, url, headers=headers, json=json, **session_request_kwargs)
../../.local/share/virtualenvs/AsyncDex-nRbDnH62/lib/python3.8/site-packages/vcr/stubs/aiohttp_stubs.py:257: in new_request
    if cassette.can_play_response_for(vcr_request):
../../.local/share/virtualenvs/AsyncDex-nRbDnH62/lib/python3.8/site-packages/vcr/cassette.py:255: in can_play_response_for
    request = self._before_record_request(request)
../../.local/share/virtualenvs/AsyncDex-nRbDnH62/lib/python3.8/site-packages/vcr/config.py:223: in before_record_request
    request = function(request)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

request = <Request (POST) https://api.mangadex.org/auth/login>, replacements = {'password': 'PASSWORD', 'refresh_token': 'REFRESH_TOKEN', 'username': 'USERNAME'}

    def replace_post_data_parameters(request, replacements):
        """Replace post data in request--either form data or json--according to replacements.

        The replacements should be a list of (key, value) pairs where the value can be any of:
          1. A simple replacement string value.
          2. None to remove the given header.
          3. A callable which accepts (key, value, request) and returns a string
             value or None.
        """
        if not request.body:
            # Nothing to replace
            return request

        replacements = dict(replacements)
        if request.method == "POST" and not isinstance(request.body, BytesIO):
            if request.headers.get("Content-Type") == "application/json":
                json_data = json.loads(request.body.decode("utf-8"))
                for k, rv in replacements.items():
                    if k in json_data:
                        ov = json_data.pop(k)
                        if callable(rv):
                            rv = rv(key=k, value=ov, request=request)
                        if rv is not None:
                            json_data[k] = rv
                request.body = json.dumps(json_data).encode("utf-8")
            else:
                if isinstance(request.body, str):
                    request.body = request.body.encode("utf-8")
>               splits = [p.partition(b"=") for p in request.body.split(b"&")]
E               AttributeError: 'dict' object has no attribute 'split'

../../.local/share/virtualenvs/AsyncDex-nRbDnH62/lib/python3.8/site-packages/vcr/filters.py:100: AttributeError
======================================================================================================= short test summary info =======================================================================================================
FAILED tests/test_client.py::test_login - AttributeError: 'dict' object has no attribute 'split'

This is my conftest.py:

import os

import pytest

@pytest.fixture(scope="session")
def vcr_config():
    return {
        "filter_headers": [("authorization", "AUTHORIZATION")],
        "filter_post_data_parameters": [('username', "USERNAME"),
                                        ('password', "PASSWORD"), ('refresh_token', "REFRESH_TOKEN")]
    }

@pytest.fixture
def username():
    return os.environ["asyncdex_username"]

@pytest.fixture
def password():
    return os.environ["asyncdex_password"]

@pytest.fixture
def refresh_token():
    return os.environ["asyncdex_refresh_token"]

I am using the pytest-asyncio and pytest-recording packages.