[Python] Web3.py and Python: Unable to generate valid signatures for Four.meme wallet...

Problem Description: I'm trying to authenticate with Four.meme using their wallet-based authentication system, but I keep receiving a "Signature for this request is not valid" error. I've tried multiple approaches to sign messages with my wallet's private key, but none of them produce a signature that the Four.meme API accepts.

from web3 import Web3, Account
from eth_account.messages import encode_defunct

# Setup
PRIVATE_KEY = "YOUR_PRIVATE_KEY" # Private key redacted for security
WALLET_ADDRESS = Web3.to_checksum_address("0x8358494c81a35db01AfB1EEb93cBfe995B0cF057")
web3 = Web3(Web3.HTTPProvider("https://bsc-dataseed.binance.org/"))

# Create session
session = requests.Session()
session.headers.update({
"Origin": "https://four.meme",
"Referer": "https://four.meme/",
"User-Agent": "Mozilla/5.0",
"Content-Type": "application/json"
})

# Get nonce
nonce_url = "https://four.meme/meme-api/v1/private/user/nonce/generate"
nonce_payload = {
"accountAddress": WALLET_ADDRESS,
"verifyType": "LOGIN"
}
resp = session.post(nonce_url, json=nonce_payload)
nonce = resp.json()["data"]

# Sign message
message = str(nonce) # Just the nonce as a string, without formatting
message_encoded = encode_defunct(text=message)
signed_msg = Account.from_key(PRIVATE_KEY).sign_message(message_encoded)
signature = signed_msg.signature.hex()
if not signature.startswith("0x"):
signature = "0x" + signature

# Login attempt
login_url = "https://four.meme/meme-api/v1/private/user/login/dex"
login_payload = {
"region": "WEB",
"langType": "EN",
"loginIp": "",
"inviteCode": "",
"verifyInfo": {
"address": WALLET_ADDRESS,
"networkCode": "BSC",
"signature": signature,
"verifyType": "LOGIN"
},
"walletName": "MetaMask"
}

login_resp = session.post(login_url, json=login_payload)
print(login_resp.json()) # {"code": -1006, "msg": "Signature for this request is not valid"} ```

What I've Tried

Different message formats:

Just the nonce as a string: "123456"
Formatted message: "Login Four.Meme:\n\n123456"
Hex-encoded nonce
UTF-8 encoded bytes


Different signature methods:

Using encode_defunct() with various parameters
Different recovery ID formats (0/1 vs 27/28)
Personal sign format with Ethereum-specific prefixes


Manual signature verification:

Signed a message manually with MetaMask in the browser
Used the same nonce and signature in my script
Still received "Signature for this request is not valid"


Recovery validation:

Verified that the correct address is recovered from the signatures
Confirmed that the signature format appears correct (65 bytes with 0x prefix)



I've even tried directly copying a successful signature from a browser connection, but it's still rejected when coming from my script.
Environment

Python 3.10
web3.py 6.0.0
Binance Smart Chain
MetaMask for browser comparison

Question
What could be causing the "Signature for this request is not valid" error when my signatures appear to be correctly formatted and recover to my wallet address? Are there specific requirements for Four.meme's signature validation that I'm missing?

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