Blockchain technology is being developed rapidly in recent years. It has been applied to stock trading, supply chain auditing, crowd-funding, energy trading, and Internet-of-Things. Specifically, in Internet-of-Things applications, how the data is transmitted before reaching a blockchain platform reliably is a challenging issue. In this paper, we focus on an energy trading scenario with Internet-of-Things blockchain applications for energy trading. In this scenario, energy generated from renewable sources can be traded in a peer-to-peer manner among micro-grids. This requires a high level of data communication reliability. Blockchain is adopted as an effective decentralized transaction management solution. In particular, we propose a proof-of-concept for reliable data transmission from smart meters to the blockchain based on Sigfox technology and the Ethereum. To enhance reliability, we configure the base station antenna as a block-based mode and propose a physical data layer for wireless communication. We perform extensive experiments to evaluate the performance of the proposed wireless communication system for the blockchain.