Hi @Riccardodg, welcome to the community!
If you have a specific URL for each email, you can upload that into one of your Klaviyo Lists and assign it a Custom Property field name. Klaviyo has a good documentation on how to upload emails with custom properties here:
Then, you can use the personalization tag in your Campaign (or Flow Message) Email Template like you use any custom property in a template. In this case, the field name is “Custom-URL” - but of course you can name this field whatever you want. There’s also a “default” value in the event that a Profile doesn’t have this field value.
{{ person|lookup:'Custom-URL'|default:'some default URL' }}
Hope that helps!