Paypal ionic v3

I can not implement the paypal payment in my app,
when I invoke the paypal function, the following error occurs
Object (…) is not a function
I have already changed the file json package.json the field
“@ ionic-native / paypal”: “5.0.0-alpha.3”,
and if I give the command “npm install”
the following error comes out to me
npm WARN @ ionic-native / paypal @ 5.0.0-alpha.3 requires a peer of @ ionic-native / core @ 5.0.0-alpha.3 but none is installed. You must install peer dependencies yourself.
thanks for any help