Variables in script are not parsed, they are evaluated. So it should be treated as if it were real Javascript variables.
So, if you write "{{My variable}}", it will parse the variable ID (something like vclfqgqkdf000008mh3r6xakty). You need to remove the double quotes to properly get the variable content value.
For example,
❌ "{{URL base}}/path" => vclfqgqkdf000008mh3r6xakty/path
✅ {{URL base}} + '/path' =>
https://domain.com/path✅
${{{URL base}}}/path =>
https://domain.com/path
