I've just installed the nuget package for EPiServer.Social (v2.2.2) on my local episerver installation (episerver.cms 10.3.2). Then in social reach tab> settings, I've added a facebook channel and authorized it and then I've created a message. Everything worked fine, but then when I went to overview tab I saw that the message has failed.

Any Idea why get_SiteUrl throws exception?

Do I need to set any configuration in web config?

Do I need to set anything for workflows on Episerver 10? 

This is the log:

2017-02-13 13:24:48,590 [16] ERROR EPiServer.Social.MessageBusiness: Error while executing to send social messages
System.NullReferenceException: Object reference not set to an instance of an object.
at EPiServer.Social.Configuration.SettingsElement.get_SiteUrl()
at EPiServer.Social.Helpers.UrlUtil.MakeAbsoluteUrl(String url)
at EPiServer.Social.Helpers.UrlUtil.ConvertToExternalUrl(String internalUrl)
at EPiServer.Social.Providers.FacebookProvider.Send(SocialMessageDto socialMessage)
at EPiServer.Social.MessageBusiness.<>c__DisplayClass15_0.b__0()
System.NullReferenceException: Object reference not set to an instance of an object.
at EPiServer.Social.Configuration.SettingsElement.get_SiteUrl()
at EPiServer.Social.Helpers.UrlUtil.MakeAbsoluteUrl(String url)
at EPiServer.Social.Helpers.UrlUtil.ConvertToExternalUrl(String internalUrl)
at EPiServer.Social.Providers.FacebookProvider.Send(SocialMessageDto socialMessage)
at EPiServer.Social.MessageBusiness.<>c__DisplayClass15_0.b__0()