1.遇见“4000，服务繁忙，请稍后再试”。

检查AndroidManifest.xml中支付宝配置，多数情况是少配置了H5PayActivity或H5AuthActivity

<!-- 支付宝配置，必须 -->
<activityandroid:name="com.alipay.sdk.app.H5PayActivity"android:configChanges="orientation|keyboardHidden|navigation"android:exported="false"android:screenOrientation="behind" >
</activity>
<activityandroid:name="com.alipay.sdk.auth.AuthActivity"android:configChanges="orientation|keyboardHidden|navigation"android:exported="false"android:screenOrientation="behind" >
</activity>
<activity android:name="com.umf.pay.sdk.UmfPayActivity"android:theme="@android:style/Theme.Translucent.NoTitleBar" />
<!-- 7.0SDK增加下列声明 -->
<activityandroid:name="com.alipay.sdk.app.H5AuthActivity"android:configChanges="orientation|keyboardHidden|navigation|screenSize"android:exported="false"android:screenOrientation ="behind" >
</activity>
<!-- 支付宝END -->