Hi @Kristinn_Vikar,
I think this likely is due to the invalid compatible-with value. Looking at your capture, the x-elastic-client-meta header is also reflecting unexpected version for es= and t= which should match the version of the client you have referenced.
I've just had a quick look to see if I can reproduce this. I created a very simple client app which I added to an image which runs it based on the Microsoft mcr.microsoft.com/dotnet/runtime:6.0-alpine image. When I ran it and captured the headers it sent, they appeared as expected:
Internally the client uses reflection to grab version information on the assembly containing the IElasticLowLevelClient type; so essentially:
FileVersionInfo.GetVersionInfo(typeof(IElasticLowLevelClient).GetTypeInfo().Assembly.Location)?.ProductVersion;
This is presumably failing to return a value in your environment. Could you try adding some code to your app code and log out the values to see what you get. I want to first check if for some reason the version information is not retrieved in your environment.
var location = typeof(IElasticLowLevelClient).GetTypeInfo().Assembly.Location;
var version = FileVersionInfo.GetVersionInfo(location)?.ProductVersion;
Console.WriteLine(location); // or send to a logged etc.
Console.WriteLine(version); // or send to a logged etc.
Can you please confirm the base image and label for your client app Docker image. If possible, it would be great to see your Dockerfile for your image.