First, ensure you have access to the PostHog API. Obtain your API key from the PostHog dashboard, as this will be necessary to authenticate your requests. Navigate to your account settings in PostHog and locate the API key section.

Determine which data you need to transfer from PostHog to Redis. This could be event data, user properties, or other analytics data. Identify the API endpoints you will use to retrieve this data (e.g., `/api/events` for events data).

Use a programming language such as Python to write a script that authenticates with the PostHog API and fetches the desired data. Use the `requests` library in Python to make GET requests to the relevant PostHog API endpoints, ensuring you include your API key in the headers for authentication.

```python
import requests

api_key = 'YOUR_POSTHOG_API_KEY'
headers = {'Authorization': f'Bearer {api_key}'}

response = requests.get('https://your-posthog-instance.com/api/events', headers=headers)
data = response.json()
```

Process the data retrieved from PostHog to match the structure expected by Redis. This may involve transforming JSON objects, filtering data, or aggregating information. Ensure that the data is in a format that can be easily stored in Redis, such as key-value pairs or hashes.

Install a Redis client library in your programming environment. For Python, the `redis-py` library is commonly used. Establish a connection to your Redis server by providing the host, port, and any authentication credentials if required.

```python
import redis

r = redis.Redis(host='localhost', port=6379, db=0)
```

Iterate over the processed data and insert it into Redis using appropriate data structures. For example, use `r.set(key, value)` for simple key-value pairs or `r.hset(name, key, value)` for hashes. Ensure that you handle any potential errors during this process to prevent data loss.

```python
for event in data['results']:
event_id = event['id']
r.set(f'event:{event_id}', event)
```

After transferring the data, validate that it has been correctly stored in Redis. Retrieve a sample of the data from Redis and compare it against the original data fetched from PostHog to ensure accuracy and completeness. This can be done with simple get commands and comparison checks.

```python
stored_event = r.get('event:12345')
assert stored_event == data['results'][0], "Data mismatch error!"
```

By following these steps, you can efficiently transfer data from PostHog to Redis without relying on third-party connectors or integrations.