Custom fields missing on Workflow

Custom fields missing on Workflow

Hello,

I connected my Zoho CRM account to my Zoho Campaign. I would like to create a Workflow using some custom fields I created on Zoho CRM under Leads. 

The problem is that under "Workflows" on the "IF" dropdown" when choosing the Lead Fields I don't see ANY of my custom fields, only the default Zoho fields. Can you explain what am I missing or doing wrong? Thanks