> For the complete documentation index, see [llms.txt](https://docs.galaxypay.vn/upc/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.galaxypay.vn/upc/payment-gateway/api-specification/definitions/message-structure.md).

# Message Structure

\-      Service:                      REST API

\-      HTTP Method:            POST

\-      Content Type:             application/json

\-      The Request structure:

<table><thead><tr><th width="62">#</th><th width="123">Component</th><th width="140">Param</th><th>Description</th></tr></thead><tbody><tr><td>1</td><td><strong>Header</strong></td><td><strong>APIKey</strong></td><td><p>Key for authentication request. </p><p>Provided by GALAXY PAY.</p></td></tr><tr><td></td><td></td><td><strong>Signature</strong></td><td>Request signature, created with <mark style="color:red;"><strong>SHA256 &#x26; Salt</strong></mark></td></tr><tr><td></td><td></td><td>Accept</td><td>Accept encoding: <mark style="color:red;"><strong>application/json</strong></mark></td></tr><tr><td></td><td></td><td>Content-Type</td><td>Request content type: <mark style="color:red;"><strong>application/json</strong></mark></td></tr><tr><td>2</td><td><strong>Body</strong></td><td></td><td>JSON content</td></tr></tbody></table>