BadRequest (400) with Substatus 1001 when adding new item in Azure Cosmos DB using Microsoft.Azure.CosmosRepository library

I getting an issue while creating a new item with CreateAsync method in Azure Cosmos DB using the Microsoft.Azure.CosmosRepository(https://www.nuget.org/packages/IEvangelist.Azure.CosmosRepository) library 7.0.1 version with .NET 6 Web Api application. I am receiving a BadRequest (400) response with Substatus 1001.

Here are the details:

I have a method AddEmailTemplate that updates an email template in the repository. However, when I execute the update operation, I receive the following error:

> Cosmos query executed for item type EmailTemplate with a charge of 2.8
> RUs Query: {"query":"SELECT VALUE root FROM root WHERE
> ((((root["NotificationType"] = 3) AND (root["NotificationSubType"]
> = "")) AND (root["Language"] = "en-US")) AND ((NOT IS_DEFINED(root["Type"])) OR (root["Type"] =
> "EmailTemplate")))"} fail:
> SFH.N3.WebApi.Controllers.EmailTemplates.EmailTemplateController[0]
> An error occurred while updating email template, RequestId:338bcaa9-f8a3-418b-932b-4d88a7ab6a08
> Microsoft.Azure.Cosmos.CosmosException : Response status code does not indicate success: BadRequest (400); Substatus: 1001;
> ActivityId: 5242793b-f785-436d-9565-5d7c1e730ef4; Reason: ();
> at Microsoft.Azure.Cosmos.ResponseMessage.EnsureSuccessStatusCode()
> at Microsoft.Azure.Cosmos.CosmosResponseFactoryCore.ProcessMessage[T](ResponseMessage
> responseMessage, Func2 createResponse)
> at Microsoft.Azure.Cosmos.ContainerCore.CreateItemAsync[T](T item, ITrace trace, Nullable1 partitionKey, ItemRequestOptions
> requestOptions, CancellationToken cancellationToken)
> at Microsoft.Azure.Cosmos.ClientContextCore.RunWithDiagnosticsHelperAsync[TResult](String
> containerName, String databaseName, OperationType operationType,
> ITrace trace, Func2 task, Func2 openTelemetry, String operationName,
> RequestOptions requestOptions)
> at Microsoft.Azure.Cosmos.ClientContextCore.OperationHelperWithRootTraceAsync[TResult](String
> operationName, String containerName, String databaseName,
> OperationType operationType, RequestOptions requestOptions, Func2
> task, Func2 openTelemetry, TraceComponent traceComponent, TraceLevel
> traceLevel)
> at Microsoft.Azure.CosmosRepository.DefaultRepository`1.CreateAsync(TItem
> value, CancellationToken cancellationToken)

private async Task AddEmailTemplate(AddEmailTemplateCommand command)
        {
            var emailTemplateExist = await _repository
                .GetAsync(x => x.NotificationType == command.NotificationType
                && x.NotificationSubType == command.NotificationSubType
                && x.Language == command.Language).FirstOrDefaultAsync();
            // Insert email template
            if (emailTemplateExist == null)
            {
                var emailTemplate = new EmailTemplate
                {
                    Id = Guid.NewGuid().ToString(),
                    NotificationType = command.NotificationType,
                    NotificationSubType = command.NotificationSubType,
                    EmailSubject = command.EmailSubject,
                    Language = command.Language,
                    TemplateId = command.TemplateId,
                };
                await _repository.CreateAsync(emailTemplate);
            }
            else
            {
                string message = $"Email template already exists for the specified notification type:{command.NotificationType}";
                _logger.LogWarning(message);
                throw new EmailTemplateAlreadyExistsException(message);
            }
        }

EmailTemplate class:

[Container(nameof(EmailTemplate))]
    [PartitionKeyPath("/NotificationType")]
    public class EmailTemplate : Item
    {
       
        [JsonProperty(PropertyName = "NotificationType")]
        public int NotificationType { get; set; }
        [JsonProperty(PropertyName = "NotificationSubType")]
        public string NotificationSubType { get; set; }
        [JsonProperty(PropertyName = "Language")]
        public string Language { get; set; }
        [JsonProperty(PropertyName = "TemplateId")]
        public string TemplateId { get; set; }
        [JsonProperty(PropertyName = "EmailSubject")]
        public string EmailSubject { get; set; }
        protected override string GetPartitionKeyValue() => NotificationType.ToString();
       
        [JsonProperty(PropertyName = "_ts")]
        public long Timestamp { get; set; }
       
        [JsonIgnore]
        public DateTime TimestampAsDateTime => DateTimeOffset.FromUnixTimeSeconds(Timestamp).DateTime;
    }

appsettings.json:

"RepositoryOptions": {
    "CosmosConnectionString": "AccountEndpoint={CosmosDbConnectionString}",
    "DatabaseId": "TestDb",
    "OptimizeBandwidth": true,
    "ContainerPerItemType": true,
    "AllowBulkExecution": true,
    "SerializationOptions": {
      "IgnoreNullValues": true,
      "PropertyNamingPolicy": "Default"
    }
  }

Cosmos Db Container:

I would appreciate any insights or suggestions on how to resolve this issue. Is there any specific meaning for Substatus 1001 in this context? How can I further investigate and resolve this error?

But GetAsync method is working fine, when I am retrieving the existing items (var emailTemplates = await _repository.GetAsync("{query}");

Based on the documentation for that error code: https://learn.microsoft.com/azure/cosmos-db/nosql/troubleshoot-bad-request#wrong-partition-key-value

It means the Partition Key is incorrectly specified. There is a mismatch between the Container's Partition Key Definition and the property being send as Partition Key.

Double check on the Container's Partition Key Definition if it's indeed /NotificationType and if the NotificationType property has a correct supported value type.