The former Pachuca striker is joining the Hammers in a £12 million deal.
"I'm happy to join a very good team," Enner Valencia told a Mexican radio station.
"There were a few issues with some parts of the contract but all parties involved have now reached an agreement.
"Antonio Valencia has helped a lot in my decision. It is a good team and the people are very friendly."
Valencia has penned a five-year contract.
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