Creation of custom variables is possible when importing a list of contacts.
First, go to the People page, then click the + button in the top-right corner of your screen and choose Import from CSV.
Upload your prospect list from a CSV-file and Reply will ask you to match your data with column fields. You'll need to scroll down to see all data fields available for mapping.
Match the new variable with the data column of your CSV file and press Continue.
You're done! When this is done, simply hit the Import button and manage your list of prospects with custom variables. You can create as many custom variables as you need to and use them in Templates (email bodies and subject lines), Steps or Preview sections.
You can also filter your people by custom variable when creating a smart filter
To add custom fields through our API, check out this article.