ERC1155 Validation Error code: -32000

Question

I am using web3py to make a transaction. But I am getting validation error:

{'message': 'VM Exception while processing transaction: revert Need operator approval for 3rd party transfers.', 'code': -32000, 'data': {'stack': 'RuntimeError: VM Exception while processing transaction: revert Need operator approval for 3rd party transfers.\n at Function.RuntimeError.fromResults (/Applications/Ganache.app/Contents/Resources/static/node/node_modules/ganache-core/lib/utils/runtimeerror.js:89:13)\n at module.exports (/Applications/Ganache.app/Contents/Resources/static/node/node_modules/ganache-core/lib/utils/gas/guestimation.js:142:32)', 'name': 'RuntimeError'}}

Can someone please help me understand this error? Why is it happening? I am using function safeTransferFrom (from ERC1155)

Thank you.

Answer 1

If we refer to the doc (https://github.com/ethereum/EIPs/blob/master/EIPS/eip-1155.md), we can read in the definition of the safeTransferFrom function :

Caller must be approved to manage the tokens being transferred out of the _from account

The user passed to the _from parameter of safeTransferFrom has therefore to first approve the caller using setApprovalForAll(address _operator, bool _approved) with :

• _operator the address of the safeTransferFrom caller which can be either an EOA or a smart contract
• _approved set to true.

To resume:

1. UserA approves UserB/smart contract and authorizes him/it to transfer his funds
2. The approved UserB/smart contract can now transfer the funds of UserA
3. UserA can "disapprove" at any time UserB/smart contract by sending a new setApprovalForAll transaction with _approved set to false.

Answer 2

If you're just looking to transfer tokens from your own address, make sure you specify your own address as first parameter in safeTransferFrom.

If you're trying to send tokens on behalf of a user, the user needs to approve the transaction first, before you can send a transaction through a smart contract with safeTransferFrom. To do this, the user needs to call setApprovalForAll(address _operator, bool _approved) with the address of the operator (usually a smart contract), and a boolean to indicate if the operator is approved or not.

After that you will be able to transfer tokens on behalf of a user, using safeTransferFrom. You cannot call setApprovalForAll from a smart contract, for a user. The user needs to explicitly call this function for themselves.