Что то сделал

Bank/BankDatabaseImplement/Implements/OperationStorage.cs

@@ -55,6 +55,11 @@ namespace BankDatabaseImplement.Implements
 		{
 			using var context = new BankDatabase();
 			var operation = context.Operations.Include(x => x.SenderCard).Include(x => x.RecipientCard).Include(x => x.Transfer).FirstOrDefault(x => x.Id == model.Id);
+			var transfer = context.Transfers.FirstOrDefault(x => x.OperationId == model.Id);
+			if (transfer != null)
+			{
+				return null;
+			}
 			if (operation == null)
 			{
 				return null;
@@ -67,6 +72,11 @@ namespace BankDatabaseImplement.Implements
 		{
 			using var context = new BankDatabase();
 			var operation = context.Operations.Include(x => x.SenderCard).Include(x => x.RecipientCard).Include(x => x.Transfer).FirstOrDefault(rec => rec.Id == model.Id);
+			var transfer = context.Transfers.FirstOrDefault(x => x.OperationId == model.Id);
+			if (transfer != null)
+			{
+				return null;
+			}
 			if (operation != null)
 			{
 				context.Operations.Remove(operation);

Bank/BankDatabaseImplement/Implements/RequestStorage.cs

@@ -73,7 +73,11 @@ namespace BankDatabaseImplement.Implements
 				var Request = context.Requests.FirstOrDefault(rec => rec.Id == model.Id);
 				if (Request == null)
 				{
-					return null;
+					throw new Exception("Заявка не найдена");
+				}
+				if (Request.Status != RequestStatus.Принята)
+				{
+					throw new InvalidOperationException("Заявка уже выполнена");
 				}
 				Request.Update(model);
 				context.SaveChanges();
@@ -93,6 +97,10 @@ namespace BankDatabaseImplement.Implements
 			var element = context.Requests
 			.Include(x => x.Cards)
 			.FirstOrDefault(rec => rec.Id == model.Id);
+			if (element?.Status != RequestStatus.Принята)
+			{
+				return null;
+			}
 			if (element != null)
 			{
 				context.Requests.Remove(element);

Bank/BankDatabaseImplement/Models/Request.cs

@@ -57,11 +57,11 @@ namespace BankDatabaseImplement.Models
 			Sum = model.Sum;
 		}
 
-		public bool ChangeStatus(RequestStatus status)
+		public bool Execute()
 		{
 			if(Status == RequestStatus.Принята)
 			{
-				Status = status;
+				Status = RequestStatus.Выполнена;
 				return true;
 			}
 			return false;