--Создание таблички
CREATE TABLE [dbo].[EmpInfo](
	[EmpID] [int] NULL,
	[NatID] [nvarchar](max) COLLATE Cyrillic_General_BIN2 ENCRYPTED WITH (COLUMN_ENCRYPTION_KEY = [ColomnKey], ENCRYPTION_TYPE = Randomized, ALGORITHM = 'AEAD_AES_256_CBC_HMAC_SHA_256') NULL,
	[Amount] [decimal](18, 2) ENCRYPTED WITH (COLUMN_ENCRYPTION_KEY = [ColomnKey], ENCRYPTION_TYPE = Randomized, ALGORITHM = 'AEAD_AES_256_CBC_HMAC_SHA_256') NULL
) ON [PRIMARY]
GO

//Пример кода, который строит SqlCommand.
command.CommandText = "INSERT INTO EmpInfo(EmpID, NatID, Amount) VALUES (@key, @ssn, @amount)";

command.Parameters.AddWithValue("@key", key);
command.Parameters.AddWithValue("@ssn", DBNull.Value);
command.Parameters.AddWithValue("@amount", Convert.ToDecimal("11.00"));
command.ExecuteNonQuery();

Operand type clash: decimal(4,2) encrypted with (encryption_type = 'RANDOMIZED', encryption_algorithm_name = 'AEAD_AES_256_CBC_HMAC_SHA_256', column_encryption_key_name = 'ColomnKey', column_encryption_key_database_name = 'ZP_Test') is incompatible with decimal(18,2) encrypted with (encryption_type = 'RANDOMIZED', encryption_algorithm_name = 'AEAD_AES_256_CBC_HMAC_SHA_256', column_encryption_key_name = 'ColomnKey', column_encryption_key_database_name = 'ZP_Test')
Statement(s) could not be prepared.

exec sp_describe_parameter_encryption N'INSERT INTO EmpInfo(EmpID, NatID, Amount, AmountDec) VALUES (@key, @ssn, @amount, @amountDec)',N'@key int,@ssn nvarchar(7),@amount decimal(4,2)'