Can EcoFlow refuse warranty from eBay item?

I bought an EcoFlow River Max Power Station 512WH X-boost (pictured) from an eBay seller for £336.83. Although it works well enough, charging it requires a 240-volt supply, which means I can’t use an in-car charger or solar panels. This makes it useless for our motor home. I contacted the eBay seller but received no reply, and EcoFlow won’t help under the warranty. Yes, EcoFlow can refuse to help because Andy bought the power station from a private seller, not an authorised retailer. This invali...