NU1301: The local source doesn't exist

[Noggog]

Synthesis has a blocking error stating NU1301: the local source doesn't exist

[Noggog]

Nuget is the system that downloads all the libraries the patchers use to run. It uses a Nuget.Config file which is automatically created for you when installing the SDK as part of the installation phase of Synthesis. This should generally work out of the box without needing to tinker with anything.

However, other applications/systems might've added extra entries on it that aren't happy. For example:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
    <add key="SomeExtraEntry" value="C:\Some\NonExistent\Folder" />
  </packageSources>
</configuration> 

C:\Some\NonExistent\Folder doesn't exist, and so error 1301 is yelling about it.

Open your Nuget.Config and double check the entries make sense. By default, the config only comes with the official nuget.org entry.
The config file is typically located in your %appdata%/NuGet folder