[Integrating with ZoHo CRM] field mapping missing a dozen fields from CRM

[Integrating with ZoHo CRM] field mapping missing a dozen fields from CRM

Hi, I am trying to integrate a form into ZoHo CRM - specifically into the 'leads' module - but a bunch of the fields in the CRM are not appearing in the drop-down box. All of the fields from the form are there. Is their a limit to how many fields can be mapped or something?