Cosmos DB provider in Entity Framework Core throwing 400 BadRequest

I've integrated Cosmos DB in my ASP.NET Core API project, using the latest EF Core package that ships with a Cosmos DB provider.

I'm able to successfully use this provider when running locally in my local ASF cluster, connecting to a local Cosmos DB emulator instance. However, when trying to either run in local ASF or Azure-hosted ASF, I'm unable to connect to the Azure Cosmos DB instance. For some reason I keep getting a 400 BadRequest when initializing the seed for the database/collection.

It's the following line that is generating an error:

var created = await context.Database.EnsureCreatedAsync();

Exception:

BadRequest at Microsoft.EntityFrameworkCore.Cosmos.Storage.Internal.CosmosClient.CreateDocumentCollectionIfNotExistsOnceAsync(DbContext _, String collectionId, CancellationToken cancellationToken)
at Microsoft.EntityFrameworkCore.Storage.ExecutionStrategy.ExecuteImplementationAsync[TState,TResult](Func4 operation, Func4 verifySucceeded, TState state, CancellationToken cancellationToken)
at Microsoft.EntityFrameworkCore.Storage.ExecutionStrategy.ExecuteImplementationAsync[TState,TResult](Func4 operation, Func4 verifySucceeded, TState state, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.Cosmos.Storage.Internal.CosmosDatabaseCreator.EnsureCreatedAsync(CancellationToken cancellationToken) at Infrastructure.SystemDataContextSeed.SeedAsync(SystemDataContext context) in Infrastructure\SystemDataContextSeed.cs:line 21 at xtensions.IWebHostExtensions.Seed(IWebHost webhost) in Extensions\IWebHostExtensions.cs:line 23 at Api.<>c__DisplayClass1_0.b__1(String url, AspNetCoreCommunicationListener listener) in AccountApi.cs:line 47 at Microsoft.ServiceFabric.Services.Communication.AspNetCore.AspNetCoreCommunicationListener.OpenAsync(CancellationToken cancellationToken) at Microsoft.ServiceFabric.Services.Runtime.StatelessServiceInstanceAdapter.OpenCommunicationListenersAsync(CancellationToken cancellationToken)

What I've tried:

• Analysing log analytics, shows no logging for these requests
• Removing the EnsureCreated and just directly insert data
• Create the collection manually (SystemDataContext)
• Create the database manually (AccountService)
• Removing networking firewall (Allow all networks) in azure

The endpoint details used are in the form of:

"Cosmos": {
    "EndPoint": "https://xxxx-sqlapi.documents.azure.com:443",
    "AuthKey": "xxx==",
    "DatabaseName": "AccountService"
  },

Extension method to hook up the Cosmos DB provider:

public static IServiceCollection AddCosmosSettings(this IServiceCollection services, IConfiguration configuration)
        {
            services.AddEntityFrameworkCosmos()
                   .AddDbContext<SystemDataContext>(options =>
                   {
                       options.UseCosmos(configuration["Cosmos:EndPoint"], configuration["Cosmos:AuthKey"], configuration["Cosmos:DatabaseName"]); ;
                   },
                       ServiceLifetime.Scoped  //Showing explicitly that the DbContext is shared across the HTTP request scope (graph of objects started in the HTTP request)
                   );

            return services;
        }

Any ideas are greatly appreciated!