[From string (line 15) ]                                                                            
                                                                                                    
@startuml                                                                                           
actor Bob #red                                                                                      
participant Alice                                                                                   
participant "I have a really\nlong name" as L #99FF99                                               
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
sprite $ma_door #material2.1.19#door:ma_door                                                        
                                                                                                    
skinparam folderBackgroundColor<<MA DOOR>> White                                                    
rectangle "<color:Purple><$ma_door{scale=1}></color>\r Public key" as setup_public_key <<MA DOOR>>{}
^^^^^                                                                                               
 Syntax Error? (Assumed diagram type: sequence)