# Installing Upzelo
## 1. Insert the Upzelo JS Snippet
The following code will add the Upzelo client-side script and make itself available in the global JS namespace as `window.upzelo`. Place the following snippet into your `` element.
```html
```
{% hint style="info" %}
You can find your App ID [here](https://upzelo.com/app/developer/api-keys)
{% endhint %}
## 2. Server-side authentication
{% hint style="warning" %}
This is only required if you wish for Upzelo to take action on your behalf with your payment provider.
{% endhint %}
Server-side authentication is in place to make sure that any requests Upzelo makes to your payment provider on your behalf are authorised and legitimate. This is achieved by you generating an HMAC hash (SHA256 algorithm) with the `customerId` and your `retentionAPI` key.
{% hint style="info" %}
You can find your retentionAPI key [here](https://upzelo.com/app/developer/api-keys)
{% endhint %}
When Upzelo makes a request, it will compare the HMAC hash sent with one that is generated on our servers to ensure that the request is legitimate. Below are some examples of how this hash can be generated in different backend languages.
{% tabs %}
{% tab title="PHP" %}
```php
{
// Upzelo Config object.
const config = {
// The customer's ID from the subscription platform
customerId: 'cus_1234',
// The customer's subscription ID from the subscription platform
subscriptionId: 'sub_1234',
// The HMAC hash generated in step 2
hash: 'bd9d2eca979333103b3d93a80e8efcbd0f8421813fdb9feefffde2206b4115e8',
// The type of flow to serve
type: 'full',
// The mode that we are working with.
mode: 'live',
};
window.upzelo.open(config);
});
```
---
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```
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```
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