diff --git a/README.md b/README.md
index 93e4240e..f2ca848f 100644
--- a/README.md
+++ b/README.md
@@ -60,32 +60,85 @@ client.set_api_creds(client.create_or_derive_api_creds())
 
 ### Start trading (proxy wallet)
 
-For email/Magic or browser wallet proxies, you need to specify two additional parameters:
-
-#### Funder Address
-The **funder address** is the actual address that holds your funds on Polymarket. When using proxy wallets (email wallets like Magic or browser extension wallets), the signing key differs from the address holding the funds. The funder address ensures orders are properly attributed to your funded account.
+For email/Magic or browser wallet proxies, you need to specify two additional parameters. **Critical: The most common mistake is confusing which address goes in `key` vs `funder`.**
 
 #### Signature Types
 The **signature_type** parameter tells the system how to verify your signatures:
-- `signature_type=0` (default): Standard EOA (Externally Owned Account) signatures - includes MetaMask, hardware wallets, and any wallet where you control the private key directly
-- `signature_type=1`: Email/Magic wallet signatures (delegated signing)
-- `signature_type=2`: Browser wallet proxy signatures (when using a proxy contract, not direct wallet connections)
+
+- `signature_type=0` (default): **EOA (Externally Owned Account)** - MetaMask, hardware wallets, any wallet where you directly control the private key
+  - `key`: Your wallet's private key
+  - `funder`: Your wallet's address (or omit - defaults to signer address)
+
+- `signature_type=1`: **Polymarket Proxy** - Email/Magic wallets with Polymarket's proxy system  
+  - `key`: Your wallet's private key (the one that controls the proxy)
+  - `funder`: The proxy contract address (where your funds are held)
+
+- `signature_type=2`: **Gnosis Safe Proxy** - 1-of-1 Gnosis Safe where you're the sole owner
+  - `key`: **EOA private key that OWNS the Gnosis Safe** (not the Safe's address)
+  - `funder`: **The Gnosis Safe contract address** (where your funds are held)
+
+#### ⚠️ Common "Invalid Signature" Mistakes
+
+**For signature_type=2 (Gnosis Safe):**
+- ❌ **Wrong:** `key=safe_address, funder=eoa_address` 
+- ✅ **Correct:** `key=eoa_private_key, funder=safe_address`
+
+**The private key must be from the EOA that owns/controls the proxy, and funder must be the proxy contract address itself.**
+
+#### Funder Address
+The **funder address** is where your funds are actually held on Polymarket:
+- **EOA mode:** Your wallet address (usually auto-detected)
+- **Proxy mode:** The proxy contract address (not your EOA address)
+
+#### Troubleshooting "Invalid Signature" Errors
+
+If you get "invalid signature" errors with proxy mode:
+
+1. **Verify your setup:**
+   - For signature_type=2: private_key = EOA that owns the Safe, funder = Safe address
+   - For signature_type=1: private_key = EOA that controls the proxy, funder = proxy address
+
+2. **Test with EOA mode first:**
+   ```python
+   # Test that your private key works at all
+   client = ClobClient(HOST, key=PRIVATE_KEY, chain_id=CHAIN_ID, signature_type=0)
+   # Should get "not enough balance/allowance" error, not "invalid signature"
+   ```
+
+3. **Verify proxy ownership:**
+   - For Gnosis Safe: Check that your EOA is the sole owner of the 1-of-1 Safe
+   - For Polymarket proxy: Verify the proxy is properly linked to your EOA
 
 ```python
 from py_clob_client.client import ClobClient
 
 HOST = "https://clob.polymarket.com"
 CHAIN_ID = 137
-PRIVATE_KEY = "<your-private-key>"
-PROXY_FUNDER = "<your-proxy-or-smart-wallet-address>"  # Address that holds your funds
+
+# Example 1: Polymarket Proxy (signature_type=1)
+EOA_PRIVATE_KEY = "<your-eoa-private-key>"  # EOA that controls the proxy
+POLYMARKET_PROXY_ADDRESS = "<proxy-contract-address>"  # Where your funds are held
 
 client = ClobClient(
-    HOST,  # The CLOB API endpoint
-    key=PRIVATE_KEY,  # Your wallet's private key
-    chain_id=CHAIN_ID,  # Polygon chain ID (137)
-    signature_type=1,  # 1 for email/Magic wallet signatures
-    funder=PROXY_FUNDER  # Address that holds your funds
+    HOST,
+    key=EOA_PRIVATE_KEY,  # The EOA key that controls the proxy
+    chain_id=CHAIN_ID,
+    signature_type=1,  # Polymarket proxy
+    funder=POLYMARKET_PROXY_ADDRESS  # The proxy contract (not your EOA)
+)
+
+# Example 2: Gnosis Safe Proxy (signature_type=2)  
+SAFE_OWNER_PRIVATE_KEY = "<eoa-owner-private-key>"  # EOA that owns the 1-of-1 Safe
+GNOSIS_SAFE_ADDRESS = "<safe-contract-address>"  # Your Gnosis Safe address
+
+client = ClobClient(
+    HOST,
+    key=SAFE_OWNER_PRIVATE_KEY,  # Private key of the Safe owner (EOA)
+    chain_id=CHAIN_ID,
+    signature_type=2,  # Gnosis Safe proxy
+    funder=GNOSIS_SAFE_ADDRESS  # The Safe contract address
 )
+
 client.set_api_creds(client.create_or_derive_api_creds())
 ```
 
diff --git a/py_clob_client/order_builder/builder.py b/py_clob_client/order_builder/builder.py
index 64fb7c96..fe25f9c8 100644
--- a/py_clob_client/order_builder/builder.py
+++ b/py_clob_client/order_builder/builder.py
@@ -2,11 +2,14 @@
 from py_order_utils.signer import Signer as UtilsSigner
 from py_order_utils.model import (
     EOA,
+    POLY_PROXY,
+    POLY_GNOSIS_SAFE,
     OrderData,
     SignedOrder,
     BUY as UtilsBuy,
     SELL as UtilsSell,
 )
+import logging
 
 from .helpers import (
     to_token_decimals,
@@ -47,6 +50,39 @@ def __init__(self, signer: Signer, sig_type=None, funder=None):
         # Used for Polymarket proxy wallets and other smart contract wallets
         # Defaults to the address of the signer
         self.funder = funder if funder is not None else self.signer.address()
+        
+        # Validate proxy configuration to catch common mistakes
+        self._validate_proxy_config()
+
+    def _validate_proxy_config(self):
+        """Validate proxy configuration and warn about common mistakes."""
+        signer_address = self.signer.address().lower()
+        funder_address = self.funder.lower()
+        
+        # Check for common signature_type=2 (Gnosis Safe) mistakes
+        if self.sig_type == POLY_GNOSIS_SAFE:
+            if signer_address == funder_address:
+                logging.warning(
+                    "⚠️  Proxy configuration warning: For signature_type=2 (Gnosis Safe), "
+                    "the 'funder' should be the Safe contract address, not your EOA address. "
+                    "Current config has signer and funder as the same address. "
+                    "If you get 'invalid signature' errors, verify that:\n"
+                    "  • private_key = EOA that OWNS the Gnosis Safe\n"
+                    "  • funder = Gnosis Safe contract address\n"
+                    "See README.md troubleshooting section for more details."
+                )
+        
+        # Check for common signature_type=1 (Polymarket Proxy) mistakes  
+        elif self.sig_type == POLY_PROXY:
+            if signer_address == funder_address:
+                logging.warning(
+                    "⚠️  Proxy configuration warning: For signature_type=1 (Polymarket Proxy), "
+                    "the 'funder' should typically be the proxy contract address, not your EOA address. "
+                    "If you get 'invalid signature' errors, verify that:\n"
+                    "  • private_key = EOA that controls the proxy\n" 
+                    "  • funder = Proxy contract address\n"
+                    "See README.md troubleshooting section for more details."
+                )
 
     def get_order_amounts(
         self, side: str, size: float, price: float, round_config: RoundConfig