Zoho CRM field is disabled

Zoho CRM field is disabled

Hi,

Im trying to send a link from Zoho CRM to a contact which has a link to my zoho crm form prefilled with their details. Im following these instructions: https://help.zoho.com/portal/en/community/topic/tip-2-prefill-forms-automatically-with-existing-zoho-crm-data

Ive done everything in the article, but when the contact clicks the email link, the Zoho CRM field in the form is disabled. The contact cant type anything into it!!

What could the issue be?
Thanks