Persistent "Invalid checksum" Error After API Secret Regeneration

Issue Summary:
Getting consistent "Invalid checksum" error when converting request token to access token, even after regenerating API secret and using fresh request tokens.

App Details:
- API Key: k6uu6hybqx5qmwbb
- App Name: SSScreener ML System
- App Status: Active
- Subscription: Valid (expires Oct 15, 2025)

What I've Tried:

1. Regenerated API Secret multiple times in developer console
2. Used fresh request tokens immediately after generation
3. Verified checksum calculation using multiple MD5 calculators
4. Tested different request formats (form-data, JSON, headers)
5. Cleared browser cache and used incognito mode
6. Waited for propagation (several hours between attempts)

Technical Details:

Request Format:
POST https://api.kite.trade/session/token
Content-Type: application/x-www-form-urlencoded
X-Kite-Version: 3

Body:
api_key=k6uu6hybqx5qmwbb
request_token=[fresh_token_from_login]
checksum=[calculated_md5_hash]

Checksum Calculation:
String: api_key + request_token + api_secret
MD5 Hash: Verified correct using online calculators

Current Error:
{
"status": "error",
"message": "Invalid `checksum`.",
"data": null,
"error_type": "TokenException"
}

Timeline:
- Yesterday: System working perfectly with existing access token
- Today morning: Access token expired (normal daily expiration)
- Current: Unable to generate new access token despite multiple attempts

Questions:
1. Is there a known propagation delay for regenerated API secrets?
2. Could there be a server-side caching issue preventing new secret recognition?
3. Any additional steps required after API secret regeneration?

System was working fine until normal token expiration occurred. Any guidance would be appreciated!