How to use :splat in _redirects?

I’m trying to a site that uses only the redirects feature of Netlify. You can call it a link shortener. I am having the following URL:
I’m trying to create the redirect such that will redirect to the above link.
However, should redirect to
Basically, I want it to inject the slug into the WhatsApp API link.
Is this possible with _redirects alone or do I have to use Serverless functions?

Got it working by using the following rule in _redirects