When creating a Zap, you may want to pull in a value from a prior step—for example, to assign a task to a different person depending on variables from the trigger step. Some fields let you insert this information, but depending on the field you fill out, you may run into a static dropdown menu that doesn’t allow it. That’s where custom values come in.
You may want to create new cards in Trello on different boards depending on the data that comes through either the trigger or a previous action step.
The two types of fields you can pass to a custom value are Name fields and ID fields. When there is just a name field, you only need to pass over the name of the field. When there is an ID, the app will only accept the ID of that field. You can tell which kind of values the field accepts by reading the help text below the label. It will tell you if you need to send an ID or a name.
You can only use custom values in action steps and they are only a way to link to an option that already exists in your app. They are not a way to use a value that doesn’t exist in your app.