Guides

Why Am I Not Receiving USDC? Tips and Fixes

Safwaan

16 Jun 2023 • 3 min read

Plus: The Difference Between Coins and Tokens

In this article, I’ll explain:

The difference between a coin (ETH, BTC, etc.) and a token (ERC721, ERC1155, ERC20, etc.)
What it means to “send a token”
Why you might not be receiving any USDC

1. Coins vs Tokens: Know The Difference

Coins and tokens are used interchangeably in crypto. But they’re fundamentally different.

Coins, such as Ether (ETH) or Bitcoin (BTC), are built directly into their unique blockchains (Ethereum and Bitcoin respectively). ETH facilitates actions and transactions on Ethereum; BTC facilitates actions and transactions on Bitcoin.

Tokens, on the other hand, are built on top of existing blockchains like Ethereum, and represent assets or utilities within a specific ecosystem. They abide by certain standards, which allow them to interact smoothly within the ecosystem. Importantly, tokens require smart contracts for transacting with specific tokens.

Here are some examples of token standards:

ERC20: Standard for fungible tokens. Each token is identical to the next. A good example is the USDC (USD Coin), a stablecoin pegged to the US dollar.
ERC721: Standard for non-fungible tokens (NFTs). Each token is unique and holds different value. Azuki digital collectibles are great examples of ERC721 tokens.
ERC1155: A more advanced type of token, which can represent both fungible and non-fungible tokens within a single smart contract.

Section 2: The Process of Receiving a Token

Receiving a token like USDC isn't quite as simple as someone sending it over to you. Due to the smart contract's rules, the you play a crucial role in this process too.

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Think of transferring a native coin, such as ETH, akin to cash payment - simple and straightforward. However, transferring a token like USDC resembles using a check, which represents the cash value but needs explicit spender's permission and receiver's acceptance. Notably, no actual money changes hands. Instead, both parties' bank balances adjust to reflect the transaction, similar to how a smart contract handles balances and transaction records. The USDC contract fulfills this role, acting as the facilitating bank.

Here's a simplified view of the process

Paper - Sender sets your allowance: The sender calls the approve() function on the USDC smart contract, specifying the number of tokens they want to send you.
Your Smart Contract - You receive the tokens: You (the contract) calls the transferFrom() function on the USDC (or any ERC20) smart contract, specifying the msg.sender as the address to receive the tokens from.
Token Contract - The USDC smart contract checks the allowance set by the sender, transfers the tokens from the sender's balance to your balance, and updates the allowance.

Remember, just as the post office wouldn't hand over a package to someone else, the smart contract ensures that only the specified recipient can claim the tokens.

What to do if you’re not receiving USDC

If you're facing issues with receiving USDC tokens, here are some actionable checks you can perform:

Contract Interaction: Are you interacting with the right functions on the smart contract? Ensure you're calling the transferFrom() function correctly in your mint method.
Allowance: Have you checked if the sender (Paper) has set an allowance for the correct address? This address that is set by the sender must be the one receiving the USDC, and also the address with the function that calls the transferFrom() method. Before you attempt to transfer (withdraw) the tokens, confirm that this has been done (you can see it by looking at recent transactions for the wallet calling your contract on the block explorer).
Address Verification: Also, ensure that the allowance is set for the right receiving address. If the address you intend to receive the USDC from isn't the same as the one you registered on the contracts dashboard, this will cause a problem. A common example of this mismatch is if you registered a proxy contract in the dashboard or if the USDC receiving address is a safe wallet address. If this is the case, you can specify the receiving address in mintMethod.payment.spender as found here.

Wrap-Up

Distinguishing between coins and tokens and understanding the token transaction process is like leveling up in the crypto game. Tokens, like USDC, call for a bit more legwork—interacting with smart contracts—unlike their coin counterparts (think ETH or BTC). If USDC seems to be playing hard to get, consider giving contract interaction, allowance, and address verification a good once-over.

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