redirect to external website

[df2]

I am splitting my website and will stop selling some products. These products will continue to be sold on the same website but with an other extension. This domain wont be connected to my shopify. 

How can I redirect to this external website? 

So the main website is www.dampfabriek.com. Many products will be still visible here but will be sold solely on www.dampfabriek.nl who has an other owner than me. 

Trying to redirect on the navigation page is not working. 

[Guleria]

Hello,

You can do it with Meta fields free version app.
Use of the app that you can  set a meta fields with key and value.
e.g. Key = target_url and value = you-target-url
Once you config it after that with in a code in b/w the sold out condition change the code to target url.
In this way all the product which is sold out and have a meta field value available will redirect to the destination url.

Thanks

[df2]

Thank you so much for your quick reply. 

What should be the namespace and the type? 

[Guleria]

namespace  = any-text
type = string

[df2]

Sorry its me again. 

You say: "Once you config it after that with in a code in b/w the sold out condition change the code to target url."

What code should i enter and where exactly?