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docs/client/express.md

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+# Mpesa Express
+
+## Mpese Express Request
+
+Lipa na M-PESA online API also known as M-PESA express (STK Push/NI push) is a Merchant/Business initiated C2B (Customer to Business) Payment.
+
+Once you, our merchant integrate with the API, you will be able to send a payment prompt on the customer's phone (Popularly known as STK Push Prompt) to your customer's M-PESA registered phone number requesting them to enter their M-PESA pin to authorize and complete payment.
+
+Requires a `business_short_code` - The organization shortcode used to receive the transaction and
+returns a `MpesaExpressRequestBuilder` struct
+
+Safaricom API docs [reference](https://developer.safaricom.co.ke/APIs/MpesaExpressSimulate)
+
+### Example
+
+```rust,ignore
+use mpesa::{Mpesa, Environment};
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>>{
+    dotenvy::dotenv().ok();
+
+    let client = Mpesa::new(
+        dotenvy::var("CONSUMER_KEY").unwrap(),
+        dotenvy::var("CONSUMER_SECRET").unwrap(),
+        Environment::Sandbox,
+    );
+
+    let response = client
+        .express_request()
+        .business_short_code("174379")
+        .phone_number("254708374149")
+        .party_a("600584")
+        .party_b("174379")
+        .amount(500)
+        .try_callback_url("https://test.example.com/api")?
+        .account_ref("Test")
+        .transaction_type(mpesa::CommandId::CustomerPayBillOnline) // Optional, defaults to `CommandId::CustomerPayBillOnline`
+        .transaction_desc("Description") // Optional, defaults to "None"
+        .build()?
+        .send()
+        .await;
+
+    assert!(response.is_ok());
+
+    Ok(())
+}
+```
+
+## Mpesa Express Query
+
+M-PESA Express Query API checks the status of a Lipa Na M-PESA Online Payment.
+
+Safaricom API docs [reference](https://developer.safaricom.co.ke/APIs/MpesaExpressQuery)
+
+### Example
+
+```rust,ignore
+use mpesa::{Mpesa, Environment};
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>>{
+    dotenvy::dotenv().ok();
+
+    let client = Mpesa::new(
+        dotenvy::var("CLIENT_KEY").unwrap(),
+        dotenvy::var("CLIENT_SECRET").unwrap(),
+        Environment::Sandbox,
+    );
+
+    let response = client
+        .express_query()
+        .business_short_code("174379")
+        .checkout_request_id("ws_CO_271120201234567891")
+        .build()?
+        .send()
+        .await;
+
+    assert!(response.is_ok());
+
+    Ok(())
+}
+```