Currently, the email editor displays an "Invalid URL" error when trying to append URL parameters to a Custom Value.

For example:

Using the Custom Value alone works, and entering the complete URL directly also works. However, combining a Custom Value with additional URL parameters is not supported.

Requested Improvement:

Allow Custom Values to be used as the base URL while appending additional URL parameters in the email editor.

This would make it much easier to reuse common URLs across multiple email campaigns without creating separate Custom Values for each campaign.

It would also simplify campaign management and reduce maintenance work, especially when using shared landing pages, unsubscribe pages, and tracking URLs.