FastAGI not executing with "s" as exten

When I call FastAGI in a context that has a number for exten it works just fine but when it has “s” it will just say it completed and returned 0 but it never really ran. Here are the 2 examples:

Example 1: (this works)
exten => 1000,1,Answer
exten => 1000,2,AGI(agi://

Example 2: (this doesnt’ work)
exten => s,1,Answer
exten => s,2,AGI(agi://

Why won’t it work?