Terraform - Lambda function unable to modify - Error: error modifying Lambda Function (lamda name) configuration : ValidationException:

I have created a lambda successfully thru terraform script. But now when I run an apply it throws the following error:

    Error: error modifying Lambda Function (mylambda) configuration 
    : ValidationException: 
     status code: 400, request id: d6c28f7c-49b4-4edd-848e-a2a763242e09

This is the code:

  data "archive_file" "lambda_zip_mylambda" {
           type        = "zip"
           source_dir = "./Packages/aaa/index"
           excludes    = [ ".gitkeep" ]
           output_path = "./Packages/aaa/index/index.zip"
  }
  resource "aws_lambda_function" "mylambda" {
          description      = "-"
          function_name    = var.lambdafunctionname
          handler          = "lambda_handler"
          runtime          = "python3.8"
          filename     = data.archive_file.lambda_zip_mylambda.output_path
          source_code_hash =   
                   data.archive_file.lambda_zip_mylambda.output_base64sha256
         role             = var.lambda_role_arn
         tags             = var.lambdatags
         timeout          = 300
         memory_size      = 128
    }