After enabling an SLA-based policy in API Manager, you need to add the necessary configurations to the API specification to ensure the policy is enforced correctly. This usually involves updating the RAML specification with the required headers that define the SLA tiers and their limits. Once these changes are made, the API proxy should be redeployed to apply the new policy settings. Adding the required headers in the RAML and redeploying the API proxy ensures that the SLA policy is properly communicated and enforced by the API management system.