It's simple to push any custom field from Zapier to InputKit. Here are the steps :
1. Create the custom field in your InputKit account
In the settings : https://app.inputkit.io/#/settings/custom-fields
2. Refresh fields on Zapier
On Zapier, on the InputKit action step Send a Sequence, click on Set up action
Scroll down, you should see a Refresh fields button. Once you click on it, your custom fields will appear right away. There's no delay.
3. Push any data in the custom field
Just like you'd do with any app on Zapier, you can then push any data to your custom field.
Custom field's data are attached to the sending. You can see the data when hovering your mouse on the gray "i" icon.