@DazWilkin suggestion totally works. Just to add, there’s no restriction on variable names so your “4th try” converts to:

- assign_vars:
   assign:
     - base_url: "https://something.com/query"
     - path: "/verifications"
     - id: "2025"
- make_request:
   return: ${base_url + path + "/" + id}

Result:

"https://something.com/query/verifications/2025"

If you’d like to deep dive on this, check out the Workflows syntax cheat sheet and reserved words for an overview.