Affiliate website redirection concern

[dos0659]

First of all i want to say hi to everyone here since im a new guy!

The issue:

My website is a price comparison website. I create products and inside these products i list several shops with their priced offers from the lowest to the highest. When a customer clicks the "shop now" button to go to the desired shop a new window pops up telling the user that he is being redirected to that shop. Check the website here and click "shop now" to understand what i mean: https://www.pccdkeys.com/product/buy-world-of-warcraft-legion-cd-key-for-battlenet/

This pop up page is a custom .php called redirect.php. In order to create a unique url for each shop, we add parameters in every URL like this: /redirect.php?id=5030917189616&merchant=CDKEYS&game=4117.

The redirect.php right now is under this setting:

1. custom header 301 without destination URL (which probably is wrong)
2. it is noindex, follow in meta robots
3. the parameters: **id, merchant, game **are set to NO URL's in URL parameters in webmaster tools.

If i remove the 301 redirect from the header it will lead to 200 OK but then its a soft 404 error because the page is small and for sure i dont want 8000 of soft 404 errors because google phantom will destroy me.

Another setting was:

1. No custom header so it was 200 OK
2. noindex, nofollow (which was for extra protection from the disallow)
3. disallowed in robots.txt

Thi setting kept giving soft 404 errors in audits.

I also had it with this setting:

1. custom header 301 without destination URL
2. meta robots in index, follow
3. without disallow in robots

This setting gave me Not followed errors in google webmaster tools.

The question:

Which is the proper setting for this php page? Maybe a combination of the above?

Thanks in advance and sorry for the long post.