Error while validating the service descriptor 'ServiceType'

Question

I interject in the method but it showing exception here:

The code is extension of the services.

public static IServiceCollection AddServices(this IServiceCollection services, string ConnectionString)
            {
                services.AddRepository(ConnectionString);
                services.AddTransient<INotificationService, NotificationService>();
                services.AddTransient<ITherapistServices, TherapistServices>();
                return services;
            }
    
         public class TherapistServices : ITherapistServices
        {
           
            private readonly IUnitOfWorkRepository _unitWork;
            private readonly INotificationService _notificationService;
            
    
            public TherapistServices(IUnitOfWorkRepository unitWork, NotificationService notificationService)
            {
                _unitWork = unitWork;
                _notificationService = notificationService;
            } 

Here I wrote a method where the both of the injected items are called.

public async Task<ApproveTherapist> CreateAcceptRejectTherapist(ApproveTherapistCreateDto approveTherapist)
        {
            ApproveTherapist therapistApproveReject = _mapper.Map<ApproveTherapist>(approveTherapist);
            therapistApproveReject.ApprovedAt = DateTime.UtcNow;
            therapistApproveReject.AdminId = Convert.ToInt64(approveTherapist.AdminId);
            await _unitWork.ApproveTherapistRepositoryUnit.Add(therapistApproveReject);
            _unitWork.Complete();
    
             //Push Notification coding
             var approveEntity = _unitWork.UserRepositoryUnit.GetTherapistById(approveTherapist.TherapistId);
             if(approveEntity !=null)
             {
                 NotificationModel notificationModel = new NotificationModel();
                 notificationModel.DeviceId = approveEntity.DeviceIdToken;
                 if (approveTherapist.IsApproved == true)
                 {
                     notificationModel.Title = "Approve by Admin";
                     notificationModel.Body = "Hi Therapist your application is approved by admin";
                 }
                 else
                 {
                     notificationModel.Title = "Reject by Admin";
                     notificationModel.Body = "Hi Therapist your application is reject by admin";
                 }
                 await _notificationService.SendNotification(notificationModel);
             }
             //End Push notification coding
    
            return therapistApproveReject;
        }
    
        }
    }

In the code there is exception showing on the startup. I called the extension method on the startup page. I wrote the services on the above code and the interface called up in that file.

services.AddServices(Configuration.GetConnectionString("SMBHDBConnection")); 

The exception is given below:

InnerException = {"Error while validating the service descriptor 'ServiceType: SMBH_SERVICES.RepositoryServices.Abstract.ITherapistServices Lifetime: Transient ImplementationType: SMBH_SERVICES.RepositoryServices.Concrete.TherapistServices': Unable to resolve service for ty...

Exception image: