Issue: SESv2 send_bulk_email replacement_template_data type inconsistency and unusable in Ruby SDK

[CamiloQuezadaDev]

When using Aws::SESV2::Client#send_bulk_email, no matter the format passed to replacement_template_data (Hash or String JSON), the SDK throws the following error:

ArgumentError: unexpected value at params[:bulk_email_entries][x][:replacement_template_data]

To Reproduce

Attempt 1: Passing Hash

entries = [{
  destination: { to_addresses: ["test@example.com"] },
  replacement_template_data: { "name" => "Camilo" }
}]

client.send_bulk_email({
  from_email_address: "sender@example.com",
  default_content: {
    template: {
      template_name: "campaign_test",
      template_data: { "name" => "Default User" }.to_json
    }
  },
  bulk_email_entries: entries
})

Result:
ArgumentError: unexpected value at params[:bulk_email_entries][0][:replacement_template_data]

Attempt 2: Passing String JSON

entries = [{
  destination: { to_addresses: ["test@example.com"] },
  replacement_template_data: { "name" => "Camilo" }.to_json
}]

Result:
ArgumentError: unexpected value at params[:bulk_email_entries][0][:replacement_template_data]

Expected behavior

According to the AWS SESv2 API Reference, replacement_template_data should be a String JSON. The SDK:
• Should accept a String JSON as the API requires
• Or, if it expects a Hash (for internal serialization), accept it without throwing an error

🚨 Question

✅ Is this a bug in parameter validation in the Ruby SDK SESv2 client?
✅ What is the expected parameter type that works for replacement_template_data?

Any guidance would be highly appreciated as this is critical for production bulk email workflows.

[mullermp]

Hey - are you using the latest gem version? The error indicates that no such param value should exist, which was probably true for an older version.

[CamiloQuezadaDev]

Hey, yes – I’m using the latest version of the aws-sdk-sesv2 gem, which is 1.78.0. Let me know if there’s anything else I should check to confirm compatibility with this parameter.

[mullermp]

I see the issue. The structure should be:

replacement_email_content: {
        replacement_template: {
          replacement_template_data: "EmailTemplateData",
        },
      },

Check the example usage here: https://docs.aws.amazon.com/sdk-for-ruby/v3/api/Aws/SESV2/Client.html#send_bulk_email-instance_method

[CamiloQuezadaDev]

I read the documentation many times, but I couldn't find my mistake.
Thanks so much, my friend!