Boto3 - Unable to pass existing key pair value as parameter in cloud formation parameters list

Hello.

"KeyName" in AWS::EC2::Instance must be the name of the key pair.
For example, if the key pair already created is named "test-key", the CloudFormation template will look like this.
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-instance.html#aws-properties-ec2-instance--examples

  EC2Instance1:
    Type: AWS::EC2::Instance
    Properties:
      AvailabilityZone: us-east-2a
      ImageId: ami-0233c2d874b811deb 
      InstanceType: t2.micro
      SecurityGroups:
        - !Ref EC2SecurityGroup
      KeyName: test-key
      UserData: 
        Fn::Base64: !Sub |
          #!/bin/bash
          yum update -y
          yum install -y httpd
          systemctl start httpd
          systemctl enable httpd
          #echo "<h1>Hello from Region us-east-2a</h1>" > /var/www/html/index.html

If CloudFormation is used to create IAM resources, "CAPABILITY_IAM" must be set in the Capabilities field.
If IAM resources are not created by CloudFormation, "Capabilities" is not necessary and can be deleted.
https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/cloudformation/client/create_stack.html

import boto3
cf = boto3.client('cloudformation')
def lambda_handler(event, context):
    res = cf.create_stack(
        StackName=('SampleStack'),
        TemplateURL='https://YourObjectUrl',
        Parameters=[
            {
                'ParameterKey': 'SecurityGroupDescription',
                'ParameterValue': 'test'
            },
            {
                'ParameterKey': 'KeyName',
                'ParameterValue': 'test-key'
            }
        ],
        Capabilities=[
            'CAPABILITY_IAM'
        ]
    )