How to get related records using ID from CRM.

I want to get related contacts when I select a particular account from my Zoho_CRM field on the form I have, I have referred all the CRM tasks and I am doing exactly what they have mentioned.

output = zoho.crm.getRelatedRecords("Contacts", ("Accounts"), input.Zoho_CRM_ID);

I should get all the "Contacts" of the "Account" I select. but it gives me an error that "expected BIGINT , found STRING"

so i did this ,

output = zoho.crm.getRelatedRecords("Contacts", ("Accounts"), input.Zoho_CRM_ID.toString());

but still error remains the same.Thank you.