Console error within graphiql-ui (404 POST ERROR)

[aldd-dpulidog]

When I access the GraphiQL endpoint everything shows correct except for the console that shows this error:

In the Network tab there is no response, just the 404 error, this also happens when I query something.

This is how I add my services and graphiQL:

services.AddGraphiQl(x =>
{
    x.GraphiQlPath = "/graphiql-ui";
    x.GraphQlApiPath = "graphql";
});
services.AddSingleton<IDependencyResolver>(x => new FuncDependencyResolver(type => x.GetRequiredService(type)));
services.AddScoped<UnitMeasurement>();
services.AddScoped<UnitMeasurementRepository>();
services.AddScoped<UnitMeasurementQuery>();
services.AddScoped<UnitMeasurementSchema>();
services.AddGraphQL(x =>
{
    x.ExposeExceptions = true; //set true only in development mode. make it switchable.
}).AddGraphTypes(ServiceLifetime.Scoped);

Any help is appreciated, thanks.