Why is throwing the exception: AddMassTransit() was already called and may only be called once per container?

Question

I'm adding the configuration of Mass transit for azure service bus in my ConfigureServices. I'm using .Net6 and Mass Transit 8.0.15. I'm debugging my project ti check if I'm getting the right connection string for the azure service bus but I get an exception. This is the code I have:

public class DigitalConsultantsDataServicesModule : IServicesModule
{
    public void ConfigureServices(IServiceCollection services, IHostEnvironment environment, ConfigurationManager configuration)
    {
        services.AddDbContext<DigitalConsultantsDbContext>(options =>
        {
            options.UseSqlServer(configuration.GetConnectionString("HahnSuiteDigitalConsultants"));
            options.EnableDetailedErrors(configuration.GetValue("EfCore:HahnSuiteDigitalConsultants:DetailedErrors",
                environment.IsDevelopment()));
            options.EnableSensitiveDataLogging(configuration.GetValue("EfCore:HahnSuiteDigitalConsultants:SensitiveDataLogging",
                false));
        });

        services.AddScoped(typeof(IEntityRepository<>), typeof(DigitalConsultantsEntityRepository<>));

        //This is the configuration I added here
        services.AddMassTransit(x => x.UsingAzureServiceBus((context, configuration) =>
        {
            var connectionString = context.GetService<IConfiguration>().GetValue<string>("ServiceBus");
            configuration.Host(connectionString);
        }
        ));
    }
}

About this I'm getting the following exception:

MassTransit.ConfigurationException: 'AddMassTransit() was already called and may only be called once per container. To configure additional bus instances, refer to the documentation: https://masstransit-project.com/usage/containers/multibus.html'

This is my first time using Mass Transit and I just install it. I didn't put any other configuration so I'm not sure where should be the othe call to AddMassTransit.

Answer 1

For those with same error, as Laura Díaz mentioned in her comment, the problem was she had another call to ConfigureServices allready in the project.

Calling twice or more, it tries to register in .net dependency container the same n times which ends up in that error.