Is the "maxResults" property in AWS ECR API 'DescribeImageScanFindings' broken?

Hello, I'm using postman to call AWS ECR API 'DescribeImageScanFindings' but when I tried to use the maxResults property in DescribeImageScanFindings When I set value of maxResults over 100, it always use the default value 100 and give me "nextToken" for nextpage

Followings are the request info in my Postman:

POST: https://ecr.us-east-1.amazonaws.com/?Action=DescribeImageScanFindings
Body:
{
   "imageId": { 
      "imageDigest": "sha256:xxx"
   },
   "maxResults": 999,
   "repositoryName": "xxx"
}

Header:
Content-Type application/x-amz-json-1.1
User-Agent Postman-Collection
X-Amz-Target AmazonEC2ContainerRegistry_V20150921.DescribeImageScanFindings

AWS Signature
AccessKey xxx
SecretKey xxx
AWS Region us-east-1
Service Name ecr

I wonder if this is a known issue? Any update or answer would be appericated, thank you!