If you're getting a “-2” at the end of the URL Slug after adding an Affiliate Link, it's most likely that you have a file or an image which has the same file name as the slug used for your Affiliate Link.
You can check this on your WordPress Dashboard, under Media > Libary.
Note that this is the standard behaviour of WordPress.
When the media attachment post gets created when the file is uploaded, it will give the slug to the media attachment post and if you try to use it again, it will add the “-2” to the link to avoid clashes in slug.
To fix this, you can simply delete the media item first, then change the slug of your Affiliate Link, save it, then re-upload the media item again.