### Is there an existing issue for this? - [x] I have searched the existing issues ### Current Behavior Localstack returns http 400 for SQS messages larger than 256KiB ### Expected Behavior AWS recently increased the max SQS message and batch size to 1 MiB https://aws.amazon.com/about-aws/whats-new/2025/08/amazon-sqs-max-payload-size-1mib/ ### How are you starting LocalStack? With a docker-compose file ### Steps To Reproduce #### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`) docker run localstack/localstack #### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands) - Create a test queue aws --endpoint-url=http://localhost:4566 sqs create-queue --queue-name test-queue - Generate a payload slightly over 256KiB python3 -c "print('A' * 270000)" > big_message.txt - Send the message aws --endpoint-url=http://localhost:4566 sqs send-message \ --queue-url http://localhost:4566/000000000000/test-queue \ --message-body file://big_message.txt ### Environment ```markdown - OS: - LocalStack: LocalStack version: 4.7.1.dev17 LocalStack Docker image sha: e62a727f8 LocalStack build date: 2025-08-05 LocalStack build git hash: ``` ### Anything else? I'm working on a PR to address this