I have all the requirements.
I think someone left a wrong locale route in the packages, see: "D:\a" I don't have "D" drive.

Here's my error:

[23:20:03.640] [Il2CppAssemblyGenerator] System.AggregateException: One or more errors occurred. (Response status code does not indicate success: 404 (Not Found).) ---> System.Net.Http.HttpRequestException: Response status code does not indicate success: 404 (Not Found). at System.Net.Http.HttpResponseMessage.EnsureSuccessStatusCode() at System.Net.Http.HttpClient.GetStreamAsyncCore(HttpRequestMessage request, CancellationToken cancellationToken) --- End of inner exception stack trace --- at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions) at System.Threading.Tasks.Task1.GetResultCore(Boolean waitCompletionNotification) at System.Threading.Tasks.Task1.get_Result() at MelonLoader.Il2CppAssemblyGenerator.Extensions.DownloadFile(HttpClient client, String url, String dest) in D:\a\MelonLoader\MelonLoader\Dependencies\Il2CppAssemblyGenerator\Extensions.cs:line 10 at MelonLoader.Il2CppAssemblyGenerator.FileHandler.Download(String url, String destination) in D:\a\MelonLoader\MelonLoader\Dependencies\Il2CppAssemblyGenerator\FileHandler.cs:line 29

What game?

Hi the drive d: is on the developers pc btw. Its just show as thats where the code thats giving the error is located!

same here, i can manually download the dependecies, but don't know where to put it or will it work

Try download manually from here: https://github.com/LavaGang/Unity-Runtime-Libraries/raw/master/2021.3.42.zip
and extract all to here: YOUR GAME\MelonLoader\Dependencies\Il2CppAssemblyGenerator\UnityDependencies .
It should be something like this:

We need full logs to further diagnose your issues

Almost the same issue. All versions melon loader failed to start. Framework is updated 3 times. OS: Windows10.