Ftp.download(...) problem

#1

Hi,
i have this problem with FTP native in ionic 3 return this error with “ionic serve”
Property ‘then’ does not exist on type ‘Observable’.
In the simulator a i have this alert “this.fTP.download(…).then is not a function”

this is my code:
this.fTP.download(this.file.externalDataDirectory+‘download/’+nome, url)
.then((resDL: any)=>
console.log(‘ola’)
)
.catch((error: any) => {
console.error(error);
})

thanks.