Why does a token payment show 0 ETH on a block explorer?

A token send is a contract call

An ERC-20 token is a smart contract.⁶ The contract itself keeps track of who holds how many tokens: each balance is part of the contract's own storage.⁶

So when you send tokens, your wallet sends a transaction to the token's contract, asking it to run its transfer function.¹ Blockscout describes the usual pattern: from a wallet, to the token contract, 0 ETH, with a function call in the input data.²

That's why the real example in lesson 2 showed a value of 0 ETH, while its "Interacted With (To)" line named the SHIB token contract.⁷ The tokens appear in a separate section of the page.^7,2

The Transfer event

The ERC-20 standard says a token contract must fire a Transfer event whenever tokens move, even zero tokens.³ The event holds three things: from, to and value.³

Events are how smart contracts record what happened while they ran, so that apps outside the chain can read it.^4,8 Explorers show them on a Logs tab of the transaction page.^4,2

Each log has three parts, as Ethereum's JSON-RPC interface describes it:⁹

• Address: the contract that wrote the log.⁹
• Topics: up to four indexed values. The first, Topic0, is a hash of the event's name and input types, so it identifies which event this is.^9,4
• Data: the values that are not indexed.^9,4

In ERC-20's Transfer event, from and to are indexed and value is not.³ So the two addresses sit in the topics, and the amount sits in the data.^3,4

Who wrote the log matters

A log is only as good as the contract that wrote it. ethereum.org warns that Transfer events are produced by the token contract, so a scammer can write a contract that produces them at will.⁶

So a Transfer log proves one thing: the contract at that address said tokens moved. Always check the log's address. Lesson 5 shows how to check that a contract is the real token.^6,9

Decimals: from raw number to readable amount

Smart contracts only work with whole numbers.⁵ So a token stores a big whole number, and its decimals setting says where the decimal point goes.^5,3 Decimals only changes how the amount is shown.⁵

To get the amount people see, divide the raw number by 10 to the power of decimals.⁵

The real SHIB transfer from lesson 2 shows the same maths. Its log's data holds 53,812,600,975 followed by 18 zeros. SHIB has 18 decimals, so that is 53,812,600,975 SHIB, exactly what Etherscan shows.^7,10

Internal transactions are something else

A smart contract can also move ETH itself, as part of a transaction someone else started. Explorers call this an internal transaction.^11,12 Etherscan lists these on a separate "Internal Txns" tab.¹¹

Explorers keep these three kinds of movement apart, often on separate tabs:^13,12

This can matter for exchanges. Etherscan notes that some exchanges only spot deposits on the normal transactions tab, so ETH sent through a contract may not be credited without a manual request.¹⁶