Salesforce supports "Custom objects", which is different from "Custom fields".
Within the Unify CRM API, we include custom fields as part of the CRM response.
The "Custom objects" is something very specific from Salesforce, which can be accessed using the Proxy API.
curl --location --request GET 'https://unify.apideck.com/proxy' \
--header 'Content-Type: application/json' \
--header 'Authorization: Bearer YOUR_APIDECK_API_KEY' \
--header 'x-apideck-consumer-id: YOUR_CONSUMER_ID' \
--header 'x-apideck-app-id: YOUR_APP_ID' \
--header 'x-apideck-service-id: salesforce' \
--header 'x-apideck-downstream-url: {instance_url}/services/data/v59.0/sobjects/{objectID}'
The {instance_url} is a setting managed in Vault and automatically injected when executing the Proxy request.