diff --git a/AGENTS.md b/AGENTS.md
index 92594e8c06..d70ec25a8a 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -94,6 +94,7 @@ The policy, decided for the restructure: **troubleshooting-first.**
 - Self-contained: imports shown, env vars named, network stated in a comment. A reader copies one block and it works.
 - Bare language tag, no `title=`, no line highlighting. Use `bash` for shell (not `sh`/`shell`), `ts`/`tsx` for TypeScript (not `typescript`), `js`/`jsx` for JavaScript, `solidity`, `json`, `yaml`.
 - Every address in a code block or table carries the network name and, for tokens, the decimals: `// Celo mainnet (42220), USDC, 6 decimals`.
+- Write new and edited addresses in their EIP-55 checksummed form; get it from `cast to-check-sum-address <address>`. Mixed case with a wrong checksum breaks copied code: ethers throws `bad address checksum` and viem's `isAddress` returns `false`. Do not sweep old pages just to recase addresses; fix the ones on pages you are already editing.
 - Prefer `viem` / `wagmi` examples; they support Celo fee-currency transactions natively.
 - Testnet is **Celo Sepolia, chain ID 11142220**. Alfajores (44787) is retired — do not reference it.
 
diff --git a/build/agents/x402.mdx b/build/agents/x402.mdx
index d8c07c4e95..ade220e8b7 100644
--- a/build/agents/x402.mdx
+++ b/build/agents/x402.mdx
@@ -130,7 +130,7 @@ const routes: RoutesConfig = {
         payTo: "0xYourSellerPayoutAddress", // your wallet — receives the USDC
         price: {
           amount: "10000", // $0.01 — USDC has 6 decimals; always a string
-          asset: "0xcEBA9300f2b948710d2653dD7B07f33A8B32118C",
+          asset: "0xcebA9300f2b948710d2653dD7B07f33A8B32118C",
           extra: { name: "USDC", version: "2" }, // EIP-712 domain, must match the token
         },
       },
@@ -192,8 +192,8 @@ The Celo facilitator settles **USDC** and **USDT** via EIP-3009 `transferWithAut
 
 | Token | Address | Decimals |
 |-------|---------|----------|
-| USDC | `0xcEBA9300f2b948710d2653dD7B07f33A8B32118C` | 6 |
-| USDT | `0x48065fbbe25f71c9282ddf5e1cd6d6a887483d5e` | 6 |
+| USDC | `0xcebA9300f2b948710d2653dD7B07f33A8B32118C` | 6 |
+| USDT | `0x48065fbBE25f71C9282ddf5e1cD6D6A887483D5e` | 6 |
 
 ### Celo Configuration
 
@@ -207,7 +207,7 @@ const mainnetAccepts = {
   payTo: "0xYourSellerPayoutAddress",
   price: {
     amount: "10000", // $0.01 — USDC has 6 decimals
-    asset: "0xcEBA9300f2b948710d2653dD7B07f33A8B32118C", // Celo mainnet USDC
+    asset: "0xcebA9300f2b948710d2653dD7B07f33A8B32118C", // Celo mainnet USDC
     extra: { name: "USDC", version: "2" },
   },
 };