I had the same issue with the following error message.
Error configuring services in an external startup class.
Error configuring services in an external startup class. Microsoft.Azure.WebJobs.Extensions.EventGrid: Could not load file or assembly 'System.Net.Http, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. The system cannot find the file specified.
A host error has occurred during startup operation '2c501caa-5ef3-4ff6-a0ce-017f72d2d403'
Microsoft.Azure.WebJobs.Script: Error configuring services in an external startup class. Microsoft.Azure.WebJobs.Extensions.EventGrid: Could not load file or assembly 'System.Net.Http, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. The system cannot find the file specified.
Value cannot be null. (Parameter 'provider')
Changing the extension bundle version from [4.*, 5.0.0) to [3.*, 4.0.0) in host.json file worked for me.
host.json
"extensionBundle": {
"id": "Microsoft.Azure.Functions.ExtensionBundle",
"version": "[3.*, 4.0.0)"
},