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I've created a Ethereum smart contract and I'm playing with Zepplin library to create a ERC20 token contract and a CrowdSale contract to allow people to buy my tokens.

The token contract

pragma solidity ^0.4.24;

import "https://raw.githubusercontent.com/OpenZeppelin/openzeppelin-solidity/master/contracts/token/ERC20/ERC20.sol";

contract NourToken is ERC20 
 string public symbol = "NOR";
 string public name = "Nourreddine Token";
 uint8 public decimals = 18;
 uint256 public constant INITIAL_SUPPLY = 10000 * (10 ** uint256(decimals));

 constructor() public 
 _mint(msg.sender, INITIAL_SUPPLY);
 

The crowdsale contract

pragma solidity ^0.4.24;

import "https://raw.githubusercontent.com/OpenZeppelin/openzeppelin-solidity/master/contracts/crowdsale/Crowdsale.sol";
import "https://raw.githubusercontent.com/OpenZeppelin/openzeppelin-solidity/master/contracts/token/ERC20/ERC20.sol";

contract NourCrowdSale is Crowdsale 

 constructor (
 uint256 rate,
 address wallet,
 ERC20 token) public 
 Crowdsale(rate, wallet, token)
 

When I try to do a payment on the Crowdsale contract, the transaction is failing and I don't know why.

Here is the a sample failed transaction : https://ropsten.etherscan.io/tx/0x8777f2fa58988419bbfc22c96c50470ea242db4ea865d0e85aaa9f2dd1206dbe

Can anyone explain why it's failing ?

Thank you very much.

I figured it out myself.

The only one that can perform a token transfer is the owner of the token contract.

In my case, I was creating the contract first with another account, and passed the token address as parameter of the CrowdSale contract. So the CrowdSale contract was not the owner of the token contract.

I changed the contract like this:

pragma solidity ^0.4.24;

import "https://raw.githubusercontent.com/OpenZeppelin/openzeppelin-solidity/release-v2.0.0/contracts/crowdsale/Crowdsale.sol";
import "https://raw.githubusercontent.com/OpenZeppelin/openzeppelin-solidity/release-v2.0.0/contracts/token/ERC20/ERC20.sol";
import "browser/NourToken.sol";

contract NourCrowdSale is Crowdsale 

 constructor (
 uint256 rate,
 address wallet) public 
 Crowdsale(rate, wallet, new NourToken())

Hope it will help somebody else :-)