After discussing with our team, we decided to refuse to refund this client's money.
The reason is: When the client mentioned that they had some difficulty installing the script, we told them to provide us with data to help them. But he said he had a developer and he did not want to.Therefore, when the customer refuses our help as we have developed the script and know if there is any doubt about how to proceed we do not think we have to refund the amount!
We have more than 1000 clients which when they have problems, we solve it. Never we refuse help!