# Creating SDK Module Class

Create a module class `PayContactlessSDKModule` in the android directory extending `ReactContextBaseJavaModule` and expose all public APIs using `@ReactMethod`. 

All methods return **Promises** and JSON responses (where applicable). Some methods like `doSale` or `payWithLink` require `currencyCode`, e.g 566 is Naira Code.

A simple usage is highlighted below; 

{% hint style="info" %}
Please note that SDK `Initialization API` is different from the `start method`, and it has to be called before every other public APIs (e.g initialize, doSale). 
{% endhint %}

```kotlin
import androidx.fragment.app.FragmentActivity
import com.facebook.react.bridge.*
import com.google.gson.Gson
import com.prophius.paycontactlesssdk.*
import java.util.HashMap

class PayContactlessSDKModule(
    reactContext: ReactApplicationContext
) : ReactContextBaseJavaModule(reactContext) {

    override fun getName(): String = "PayContactlessSDKModule"

    private val activity: FragmentActivity?
        get() = reactApplicationContext.currentActivity as? FragmentActivity

    /* --------------------INIT -------------------- */

    @ReactMethod
    fun initialize(apiKey: String, merchantInfo: ReadableMap, promise: Promise) {
        android.util.Log.d("PayContactless", "BRIDGE_HIT: Method entered")

        val merchant = MerchantInfo(
            merchantInfo.getString("merchantId") ?: "",
            merchantInfo.getString("terminalId") ?: "",
            merchantInfo.getString("phoneNumber") ?: "",
            merchantInfo.getString("businessName") ?: ""
        )

        val act = reactApplicationContext.currentActivity as? FragmentActivity
        if (act == null) {
            android.util.Log.e("PayContactless", "ERROR: Activity is null")
            promise.reject("NO_ACTIVITY", "Current activity is null")
            return
        }

        act.runOnUiThread {
            android.util.Log.d("PayContactless", "UI_THREAD: Executing SDK Init")
            try {
                // Your existing MerchantInfo setup...
                PayContactlessEmbed.getInstance().initialize(apiKey, merchant, object : InitializeListener {
                    override fun onSuccess(result: String?) {
                        val out = result ?: "INITIALIZED_BUT_STRING_WAS_NULL"
                        android.util.Log.d("PayContactless", "SDK_SUCCESS: $out")
                        promise.resolve(out)
                    }
                    override fun onFailure(error: Error) {
                        android.util.Log.e("PayContactless", "SDK_FAILURE: ${error.message}")
                        promise.reject("INIT_FAILED", error.message)
                    }
                })
            } catch (e: Exception) {
                promise.reject("CRASH", e.message)
            }
        }
    }

    /* -------------------- DO SALE /PayWithCard -------------------- */

    @ReactMethod
    fun doSale(
        amount: String,
        description: String,
        currencyCode: String,
        promise: Promise
    ) {
        val act = activity
        if (act == null) {
            promise.reject("NO_ACTIVITY", "Current activity is null")
            return
        }

        act.runOnUiThread {
        //SDK call
            PayContactlessEmbed.getInstance().doSale(
                amount,
                description,
                currencyCode,
                act,
                HashMap(),
                TransactionResultListener { result ->
                    promise.resolve(Gson().toJson(result))
                }
            )
        }
    }
```