Apollo Signal exposes a versioned REST API for transactional email, contacts, audiences, webhooks, metrics, projects, and sending domains.
Base URL
Always use HTTPS. Paths in this reference already include /v1, so append them to https://api.signal.apollodeploy.com exactly as shown.
Make a request
Authenticate with a project-bound API key and send JSON when an endpoint accepts a body:
The send endpoint returns its resource directly:
There is no universal data envelope. Collection endpoints that paginate use their documented data and page or cursor fields; single-resource and mutation endpoints return their response model directly. Exports and event streams use the media type shown on their endpoint page.
Common requirements
- Send
Authorization: Bearer <key> unless an endpoint explicitly documents stream-token authentication.
- Use an API key with the permission listed under Requirements on the endpoint page.
- A key is bound to one project. A
{projectId} path must refer to that project.
- Send
Content-Type: application/json for JSON request bodies. File-import and image-upload endpoints document their multipart requirements separately.
- Treat IDs such as
email_…, con_…, seg_…, and top_… as opaque strings.
- Supply and parse timestamps as ISO 8601 values. Do not depend on a server-local timezone.
Responses
Successful writes commonly return 201 Created, successful reads and updates return 200 OK, and deletes may return 204 No Content. The endpoint page is authoritative for each response.
Errors use RFC 9457-style problem details with Content-Type: application/problem+json. See Errors before implementing retries.
Use idempotencyKey in email-send JSON bodies before retrying network failures. It is a body field, not an HTTP header.
API lifecycle
The /v1 prefix is the compatibility boundary. New optional response fields can be added without changing the version, so ignore fields your client does not recognize. A breaking contract change requires a new API version. 
