TLS Handshake Failure Java 21, Netty 4.1.107.final

Hello, one of my API client has an issue contacting my webhook endpoint. Here are the (weird) things: - They support TLS1.2 - The domain is managed by cloudflare. The TLS1.0 is deactivated. - I cannot reproduce this error with the cli open-ssl, whatever configuration I use, it always works. - They manage to send me webhook for Event A and Event B, it just fails for Event C. They use Java 21, Netty 4.1.107.final. I suspect they have different micro services for different webhooks, most of them work. I'm not a security expert. I joined a trace of the error. I guess it's safe to give my API endpoint, but maybe not on the public channel, I can PM it. My next step is to install java with that config and try to reproduce that error. They say the problem comes from our side, but we just created the endpoint and use standard cloudflare settings.