Using RestSharp Library In SSIS Script Component Raises Exception - ssis

Question

I'm building an SSIS package in VS2019 that has a Data Flow task containing a Script Component. I'm setting up that component to use the RestSharp library to call a 3rd party API. However it fails when trying to create an instance of the RestClient() class. Error message is:
Error: Exception has been thrown by the target of an invocation.
Error: Method not found: 'Void System.Text.Json.JsonSerializerOptions..ctor(System.Text.Json.JsonSerializerDefaults)'.
I don't know why it's complaining about the System.Text.JsonSerializerDefaults class. The Target Framework of the Script Component project is ".NET Framework 4.7". Not sure if that's part of the problem. This is the first time I've tried using the RestSharp library in SSIS.
Can someone help me resolve this?
string uri = "https://npiregistry.cms.hhs.gov/api/?"
+ $"number={Row.NPI}"
+ "&enumeration_type="
+ "&taxonomy_description="
+ "&first_name="
+ "&use_first_name_alias="
+ "&last_name="
+ "&organization_name="
+ "&address_purpose="
+ "&city=&state="
+ "&postal_code="
+ "&country_code="
+ "&limit="
+ "&skip="
+ "&pretty=on"
+ "&version=2.1";
var client = new RestClient(uri); // << fails!
UPDATE: This appears to be a GAC issue. If I issue this command, it says that the installation succeeds:
gacutil -i RestSharp.dll
Microsoft (R) .NET Global Assembly Cache Utility. Version 4.0.30319.0
Copyright (c) Microsoft Corporation. All rights reserved.
Assembly successfully added to the cache
However, if I try to find it in the GAC, it isn't found:
gacutil -l RestSharp.dll
Microsoft (R) .NET Global Assembly Cache Utility. Version 4.0.30319.0
Copyright (c) Microsoft Corporation. All rights reserved.
The Global Assembly Cache contains the following assemblies:
Number of items = 0
What am I doing wrong?