Alternatively, you can use the PS module I've been developing:
$> Install-Module Posh-ProGet
$> Import-Module Posh-ProGet
$> $session = New-ProGetSession -Address 'http://proget.mysite.io:8624' -ApiToken 'mytoken'
$> $feed = New-ProGetFeedObject @{Name='test-feed';FeedType='asset';Active=$true}
$> New-ProGetFeed $session $feed
$> $content = "#My File \n This is a test!"
$> New-ProGetAsset $session $feed.Name "test.md" -ContentType 'text/plain' -Content $Content
$> Get-ProGetAssets $session $feed.Name
# Name : test.md
# Parent :
# Type : application/octet-stream
# Content : http://proget.mysite.io:8624/endpoints/test-feed/content/test.md
# Created : 2021-03-30T04:36:21.59Z
# Modified : 2021-03-30T04:36:21.59Z
# Size : 27
# md5 : 25a7e1e4f8e8c8d387f3e5dde6f6f2a6
# Sha1 : c584e7c125d41a9a8123f69040f30673c66c97bd
# Sha256 : 460c44334aee7966339ad4c9c749aa67b9841dcfd7d67348fc2395a7b8adf7e4
# Sha512 : 293be0c9cfffa1c939c2b711d4165073c3efb200ed25e0adb2bf1f88d0a2343f71a62d99265aa27560630a9643124182ee9774e713bd
c468d2014681325b8e41