Hi,
You are correct in that the v3 github does not support the download.
I attempted the v2 as follows:
PS C:\WINDOWS\system32> install-package octopus.client -source https://www.nuget.org/api/v2/ -provider nuget -verbose
VERBOSE: Using the provider 'NuGet' for searching packages.
VERBOSE: Searching repository 'https://www.nuget.org/api/v2/FindPackagesById()?id='octopus.client'' for ''.
VERBOSE: Total package yield:'1' for the specified package 'octopus.client'.
VERBOSE: Performing the operation "Install Package" on target "Package 'Octopus.Client' version '4.37.0' from
'https://www.nuget.org/api/v2/'.".
The package(s) come(s) from a package source that is not marked as trusted.
Are you sure you want to install software from 'https://www.nuget.org/api/v2/'?
[Y] Yes [A] Yes to All [N] No [L] No to All [S] Suspend [?] Help (default is "N"): a
VERBOSE: Searching repository 'https://www.nuget.org/api/v2/FindPackagesById()?id='Octopus.Client'' for ''.
VERBOSE: Searching repository 'https://www.nuget.org/api/v2/FindPackagesById()?id='NETStandard.Library'' for ''.
VERBOSE: Searching repository 'https://www.nuget.org/api/v2/FindPackagesById()?id='Microsoft.NETCore.Platforms'' for
''.
<snip>...
VERBOSE: Searching repository 'https://www.nuget.org/api/v2/FindPackagesById()?id='System.Threading.Thread'' for ''.
VERBOSE: Searching repository 'https://www.nuget.org/api/v2/FindPackagesById()?id='System.Net.Http'' for ''.
VERBOSE: InstallPackage' - name='Microsoft.NETCore.Platforms', version='2.1.0',destination='C:\Program Files\PackageManagement\NuGet\Packages'
VERBOSE: DownloadPackage' - name='Microsoft.NETCore.Platforms', version='2.1.0',destination='C:\Program
Files\PackageManagement\NuGet\Packages\Microsoft.NETCore.Platforms.2.1.0\Microsoft.NETCore.Platforms.2.1.0.nupkg', uri='https://www.nuget.org/api/v2/package/Microsoft.NETCore.Platforms/2.1.0'
VERBOSE: Downloading 'https://www.nuget.org/api/v2/package/Microsoft.NETCore.Platforms/2.1.0'.
VERBOSE: Completed downloading 'https://www.nuget.org/api/v2/package/Microsoft.NETCore.Platforms/2.1.0'.
VERBOSE: Completed downloading 'Microsoft.NETCore.Platforms'.
VERBOSE: Hash for package 'Microsoft.NETCore.Platforms' does not match hash provided from the server.
VERBOSE: InstallPackageLocal' - name='Microsoft.NETCore.Platforms', version='2.1.0',destination='C:\Program Files\PackageManagement\NuGet\Packages'
VERBOSE: InstallPackage' - name='Microsoft.NETCore.Targets', version='2.1.0',destination='C:\Program Files\PackageManagement\NuGet\Packages'
VERBOSE: DownloadPackage' - name='Microsoft.NETCore.Targets', version='2.1.0',destination='C:\Program
Files\PackageManagement\NuGet\Packages\Microsoft.NETCore.Targets.2.1.0\Microsoft.NETCore.Targets.2.1.0.nupkg', uri='https://www.nuget.org/api/v2/package/Microsoft.NETCore.Targets/2.1.0'
VERBOSE: Downloading 'https://www.nuget.org/api/v2/package/Microsoft.NETCore.Targets/2.1.0'.
VERBOSE: Completed downloading 'https://www.nuget.org/api/v2/package/Microsoft.NETCore.Targets/2.1.0'.
VERBOSE: Completed downloading 'Microsoft.NETCore.Targets'.
VERBOSE: Hash for package 'Microsoft.NETCore.Targets' does not match hash provided from the server.
VERBOSE: InstallPackageLocal' - name='Microsoft.NETCore.Targets', version='2.1.0',destination='C:\Program Files\PackageManagement\NuGet\Packages'
Name Version Source Summary
---- ------- ------ -------
Microsoft.NETCore.Platforms 2.1.0 https://www.nuget.org/api/v2/ Provides runtime information required to resolve target framework, platform, and runtime specific implementat...
VERBOSE: InstallPackage' - name='System.Runtime', version='4.3.0',destination='C:\Program Files\PackageManagement\NuGet\Packages'
VERBOSE: DownloadPackage' - name='System.Runtime', version='4.3.0',destination='C:\Program Files\PackageManagement\NuGet\Packages\System.Runtime.4.3.0\System.Runtime.4.3.0.nupkg',
uri='https://www.nuget.org/api/v2/package/System.Runtime/4.3.0'
VERBOSE: Downloading 'https://www.nuget.org/api/v2/package/System.Runtime/4.3.0'.
VERBOSE: Completed downloading 'https://www.nuget.org/api/v2/package/System.Runtime/4.3.0'.
VERBOSE: Completed downloading 'System.Runtime'.
VERBOSE: Hash for package 'System.Runtime' does not match hash provided from the server.
VERBOSE: InstallPackageLocal' - name='System.Runtime', version='4.3.0',destination='C:\Program Files\PackageManagement\NuGet\Packages'
Microsoft.NETCore.Targets 2.1.0 https://www.nuget.org/api/v2/ Provides supporting infrastructure for portable projects: support identifiers that define framework and runti...
VERBOSE: InstallPackage' - name='System.Text.Encoding', version='4.3.0',destination='C:\Program Files\PackageManagement\NuGet\Packages'
VERBOSE: DownloadPackage' - name='System.Text.Encoding', version='4.3.0',destination='C:\Program
Files\PackageManagement\NuGet\Packages\System.Text.Encoding.4.3.0\System.Text.Encoding.4.3.0.nupkg', uri='https://www.nuget.org/api/v2/package/System.Text.Encoding/4.3.0'
VERBOSE: Downloading 'https://www.nuget.org/api/v2/package/System.Text.Encoding/4.3.0'.
VERBOSE: Completed downloading 'https://www.nuget.org/api/v2/package/System.Text.Encoding/4.3.0'.
VERBOSE: Completed downloading 'System.Text.Encoding'.
VERBOSE: Hash for package 'System.Text.Encoding' does not match hash provided from the server.
VERBOSE: InstallPackageLocal' - name='System.Text.Encoding', version='4.3.0',destination='C:\Program Files\PackageManagement\NuGet\Packages'
System.Runtime 4.3.0 https://www.nuget.org/api/v2/ Provides the fundamental primitives, classes and base classes that define commonly-used value and reference d...
VERBOSE: InstallPackage' - name='System.Threading.Tasks', version='4.3.0',destination='C:\Program Files\PackageManagement\NuGet\Packages'
VERBOSE: DownloadPackage' - name='System.Threading.Tasks', version='4.3.0',destination='C:\Program
Files\PackageManagement\NuGet\Packages\System.Threading.Tasks.4.3.0\System.Threading.Tasks.4.3.0.nupkg', uri='https://www.nuget.org/api/v2/package/System.Threading.Tasks/4.3.0'
VERBOSE: Downloading 'https://www.nuget.org/api/v2/package/System.Threading.Tasks/4.3.0'.
VERBOSE: Completed downloading 'https://www.nuget.org/api/v2/package/System.Threading.Tasks/4.3.0'.
<snip>...
VERBOSE: InstallPackageLocal' - name='System.Threading.Thread', version='4.3.0',destination='C:\Program Files\PackageManagement\NuGet\Packages'
System.ComponentModel.Primi... 4.3.0 https://www.nuget.org/api/v2/ Provides interfaces that are used to implement the run-time and design-time behavior of components....
VERBOSE: InstallPackage' - name='Octopus.Client', version='4.37.0',destination='C:\Program Files\PackageManagement\NuGet\Packages'
VERBOSE: DownloadPackage' - name='Octopus.Client', version='4.37.0',destination='C:\Program Files\PackageManagement\NuGet\Packages\Octopus.Client.4.37.0\Octopus.Client.4.37.0.nupkg',
uri='https://www.nuget.org/api/v2/package/Octopus.Client/4.37.0'
VERBOSE: Downloading 'https://www.nuget.org/api/v2/package/Octopus.Client/4.37.0'.
VERBOSE: Completed downloading 'https://www.nuget.org/api/v2/package/Octopus.Client/4.37.0'.
VERBOSE: Completed downloading 'Octopus.Client'.
VERBOSE: Hash for package 'Octopus.Client' does not match hash provided from the server.
VERBOSE: InstallPackageLocal' - name='Octopus.Client', version='4.37.0',destination='C:\Program Files\PackageManagement\NuGet\Packages'
System.Threading.Thread 4.3.0 https://www.nuget.org/api/v2/ Provides the System.Threading.Thread class, which allows developers to create and control a thread, set its p...
Octopus.Client 4.37.0 https://www.nuget.org/api/v2/ Octopus Deploy is an automated release management tool for modern developers and DevOps teams....
PS C:\WINDOWS\system32>
As can be seen, it was successful.
You may want to consider publishing to the v3 repository to avoid future complications.
Thanks