Get JIRA attachment public url

I am able to get attachment url by using the below url:
https://domain/rest/api/latest/issue/” + issueId + “/”
I am using the below url to download the attachment:
client.DownloadFile(new Uri(imageurl), @“D:” + fileName + “.png”);

I am able to download the attachment to my local. But it is getting corrupted.

Could you please help to get the public url of attachment.