Search on Custom Field

Search on Custom Field

We're working on an integration with the Zoho FSM API and are trying to retrieve companies based on a custom field we added to the Companies module. However, we can't find a way to filter or query records using custom fields through the API.

We have a custom field (for example, ExternalSystemID) in the Companies module that links to an external system. We want to fetch companies where this field matches a specific value using an API call.

We’ve tried using the /fsm/v1/Companies endpoint, adding query parameters manually (like ?ExternalSystemID=value), and looked for filtering options like $filter or criteria that are available in other Zoho APIs (like Zoho CRM), but nothing seems to work.

Is there a way to query or filter companies based on a custom field using the Zoho FSM API? If so, could someone share an example or point us in the right direction?

Any help would be appreciated.