I bought a refurbished Samsung FlexWash washer machine in 2019 July. In 2021 June the upper washer started to give a 1DC4 error. It means "The Inner Door is not closed". I searched it on the internet and I saw it is a common issue and a lot of people complain about it. Even there is people who bought the machine, they had the problem 2 months later.  And, there is no easy solution other than to call a service. I started to call services, which is only we can use authorized services by Samsung. And, it is way expensive. $120 to come and diagnose the issue, $95 for labor, and in case to change the part, part's cost, which is the inner door is around $300. With this math to fixing it will cost around $500. The washer machine brand new is around $1500. 

Since the problem is so common and, many people complain about it, Samsung has to step up and fix the issue without any cost to owners. This problem is not happening to wrong or false use, or by owners of the machine.