"Unable to load the service index for source" for api.nuget.org

[Noggog]

Synthesis shows a blocking error that reads:

Unable to load the service index for source https://api.nuget.org/v3/index.json
   The SSL connection could not be established, see inner exception.
   Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host..
   An existing connection was forcibly closed by the remote host.

[Noggog]

The user that had this error ended up reporting that they had an internet service provider that was blocking any dotnet connections. They solved their issue by tethering their phone which apparently did not have the same limitations.

[evildarkarchon]

That user isn't the only one getting that error. I get this error with all the patchers I try to use:
ItemTagger.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json.
I even used a vpn to make sure that it wasn't an ISP block of some kind and no dice. Interestingly, if I load the project in Visual Studio, it downloads the nuget modules just fine.

[evildarkarchon]

Did some more digging, used dotnet build and when I tried to build Synthesis Registry, here's what I got (warning: wall of text):
C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry\Synthesis.Registry.MutagenScraper.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Regis try.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry.MutagenScraper.Tests\Synthesis.Registry.MutagenScraper.Tests.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthes is\Registry\Synthesis.Registry.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry.MutagenScraper.Tests\Synthesis.Registry.MutagenScraper.Tests.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthes is\Registry\Synthesis.Registry.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry.MutagenScraper.Tests\Synthesis.Registry.MutagenScraper.Tests.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthes is\Registry\Synthesis.Registry.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry.MutagenScraper.Tests\Synthesis.Registry.MutagenScraper.Tests.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthes is\Registry\Synthesis.Registry.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry.MutagenScraper.Tests\Synthesis.Registry.MutagenScraper.Tests.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthes is\Registry\Synthesis.Registry.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry\Synthesis.Registry.MutagenScraper.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Regis try.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry\Synthesis.Registry.MutagenScraper.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Regis try.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry.MutagenScraper.Tests\Synthesis.Registry.MutagenScraper.Tests.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthes is\Registry\Synthesis.Registry.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry\Synthesis.Registry.MutagenScraper.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Regis try.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry.MutagenScraper.Tests\Synthesis.Registry.MutagenScraper.Tests.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthes is\Registry\Synthesis.Registry.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry\Synthesis.Registry.MutagenScraper.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Regis try.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry.MutagenScraper.Tests\Synthesis.Registry.MutagenScraper.Tests.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthes is\Registry\Synthesis.Registry.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry\Synthesis.Registry.MutagenScraper.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Regis try.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry.MutagenScraper.Tests\Synthesis.Registry.MutagenScraper.Tests.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthes is\Registry\Synthesis.Registry.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry\Synthesis.Registry.MutagenScraper.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Regis try.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry.MutagenScraper.Tests\Synthesis.Registry.MutagenScraper.Tests.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthes is\Registry\Synthesis.Registry.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry\Synthesis.Registry.MutagenScraper.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Regis try.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry.MutagenScraper.Tests\Synthesis.Registry.MutagenScraper.Tests.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthes is\Registry\Synthesis.Registry.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry\Synthesis.Registry.MutagenScraper.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Regis try.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry.MutagenScraper.Tests\Synthesis.Registry.MutagenScraper.Tests.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthes is\Registry\Synthesis.Registry.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry\Synthesis.Registry.MutagenScraper.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Regis try.sln] C:\Users\evild\AppData\Local\Temp\Synthesis\Registry\Synthesis.Registry.MutagenScraper.Tests\Synthesis.Registry.MutagenScraper.Tests.csproj : error NU1301: Unable to load the service index for source https://api.nuget.org/v3/index.json. [C:\Users\evild\AppData\Local\Temp\Synthes is\Registry\Synthesis.Registry.sln]

[Noggog]

Here's a stackoverflow about people having your issue. See if any of their suggestions help
https://stackoverflow.com/questions/41185443/nuget-connection-attempt-failed-unable-to-load-the-service-index-for-source/65424896#65424896

[Noggog]

Other users have seen this with Antivirus Running (#203), which might be another cause of this error