I need to set the consent field as mandatory in the Checkout
Consent fields in Chargebee cannot be set as mandatory from within the UI as it is important to allow the customer to make a decision on whether to provide consent or not. We have set it up in this manner to abide by the GDPR rules.
In order to achieve your requirements you could configure custom fields as mandatory in the account information section on the checkout page. Trust this helps. Please feel free to write back in case of further queries and I'll be happy to help.