📘
Applicative Headers
Headers directly related to your API request content and authentication.

Header	Purpose / Short Description
📦 Content-Type	Indicates format of request body (e.g., JSON).
🎯 Accept	Tells API which response format is expected (usually JSON).
🔑 Authorization	Provides API key / token for authenticated endpoints.
🛡️ Idempotency-Key	Optional; prevents duplicate operations on retry (critical for payments/payouts).

📘
Transport / HTTP Headers
Required or automatically handled by the HTTP protocol. Do not modify unless you know what you are doing.

Header	Purpose / Short Description
🖥️ Host	Identifies the server being contacted (required by HTTP/1.1).
📏 Content-Length	Size of request body in bytes (auto-calculated by client).
📝 User-Agent	Identifies client software; used for monitoring/debugging.
🔗 Connection	Controls if network connection remains open after request.

👍
Best practices

Always send Content-Type: application/json when including a JSON body.

Always send Accept: application/json to ensure consistent responses.

Always include Authorization for secured endpoints.

Use Idempotency-Key for critical operations to prevent duplicates.

Let your HTTP client handle transport headers (Host, Content-Length, Connection) automatically.

Log all request and response headers during development to simplify debugging.

Application-Level Headers (you must set them)

These headers directly affect how the API interprets your request and what it returns. You are responsible for setting them correctly.

`Content-Type`

Purpose: Tells the API how to interpret the body of your request.

Most common value:

Content-Type: application/json

📘
Why it matters

Without it, the API may not parse your request body correctly.

Some endpoints may still work, but unexpected issues (e.g. malformed JSON errors) can appear.

✅Always set this header when sending JSON bodies (e.g. POST, PUT, PATCH requests).

`Accept`

Purpose: Tells the API the format you expect in the response.

Most common value:

Accept: application/json

📘
Why it matters

Ensures the API returns JSON.

Without it, the server may default to another format (rare but possible).

✅ Always include Accept: application/json.

`Authorization`

Purpose: Carries your API key, token, or credentials.

Example:

Authorization: Bearer YOUR_API_KEY

📘
Why it matters

Required for all authenticated endpoints (all except "login").

Without it, you will receive 401 Unauthorized.

`Idempotency-Key` (if supported)

Purpose: Prevents duplicate operations (e.g. payments, payouts) when retrying a request.

Example:

Idempotency-Key: unique-string-123

📘
Why it matters
If your client retries due to a timeout or network issue, the API ensures the same operation is not executed twice.

⚙️ Transport-Level Headers (handled by HTTP clients)

These headers are required by the HTTP protocol itself. In almost all cases, your HTTP client (e.g. Postman, curl, axios, fetch) automatically sets them.

`Host`

Identifies the server you are connecting to.
Mandatory in HTTP/1.1.

Example:

Host: api.example.com

⚠️
If you remove it manually, the server will likely return 400 Bad Request.

`Content-Length`

Indicates the size (in bytes) of the request body.
Automatically calculated and added by your HTTP client when you send a body.
Incorrect values can cause truncated or rejected requests.
Do not set it manually unless absolutely necessary.

`User-Agent`

Identifies your client software; user for monitoring/debugging.

Example values:

PostmanRuntime/7.32.3
curl/8.1.2

Some APIs use it for monitoring or debugging.

✅
Keep it, or set a custom value to identify your integration.

`Connection`

Controls whether the network connection stays open after the request.

Example value:

Connection: keep-alive

Usually added automatically by the client. Rarely needs to be changed.