MCP Issues on 1.2.1

I am running 1.2.1 and following instructions to test MCP but seem to have issues getting data back and commands failing

{
 "isError": true,
 "content": [
   {
     "type": "text",
     "text": "[json.exception.type_error.302] type must be string, but is null"
   }
 ]
}