We will guide you step by step through the whole installation and configuration process.

Note: You can check current PHP version in your WHMCS. To do so, go to 'Utilities' → 'System' → 'PHP Info'.

Files in your WHMCS directory should look like this.

Move to 'Setup' → 'Addon Modules', find 'Advanced Billing' and press 'Activate' button.
Note: Skip this subsection, if you have Advanced Billing For WHMCS already installed.

In order to do that, press 'Configure', choose desired admin roles and press 'Save Changes'.

Log in to your WHMCS admin area and proceed to 'Addons' → 'Advanced Billing' → 'Settings' → 'Extensions'.
Afterwards, find 'Product Auto Upgrade' and enable the extension.

Press 'Configure' next to the extension.

Advanced Billing For WHMCS is used to collect information about hosting's resource usage.
Important: Product Auto Upgrade For WHMCS uses 'Change Package' functionality to switch the products.
Therefore it is required that the products also support this feature.

Let's move to 'Configuration' firstly.

Here you can find information such as status of a group, its name and used submodule.
What is more, you can manage groups through using buttons in 'Actions' column to prepare rules for scaling services.

Press 'Create New Group' button and a short formula will appear.

Name your new group - this name is only for your information and convenience. Then select the product that can be automatically upgraded or downgraded according to resource usage count.
Optionally, you can enable and choose configurable option group that will be used to define products options.
Save the group when it is ready.

1. 'Settings' - a place where general and client area configuration is set up.
2. 'Options' - detailed configuration of rules to scale services automatically.

• Group Name - name of a group, can be changed at any time and is visible only to the admin.
• Server Type - module type of the product allowed in the group.
• Time Interval - minimum time period between the two products changes that can be made on a single hosting.
• Notifications Time Interval - defines time between notifications sent to a client.

• Display Client Rules Configuration - shows rules of this group for clients with products configured in the group.
• Modify Rules Configuration - client can modify group rules, changes will affect their product only.
• Modify Time Interval - client can modify the minimum time between two switches on a single hosting.
• Allowed Time Interval Values - specifies what time interval a client can use (they will be displayed in the form of a dropdown menu or a textbox with a limited range).
• Enable Notifications - allows the client to enable/disable notifications.
• Modify Notifications Time Interval - allows the client to modify minimum time between two notifications.
• Allowed Notifications Time Interval Values - defines values which can be used by client.
  

Do not forget to save the configuration when it is ready.

These rules will be used by the extension to determine which service should be changed.
Service will be changed according to the parameters set in rules options if the condition of either downgrade rules or upgrade rules has been met.

Before you can do anything, you must configure the upgrade and downgarade rules.

To add a new rule, select it from a dropdown menu marked on the following screen and press 'Add'.

To add a rule which will be fulfilled when the product has more or equal than 3 FTP accounts, choose '≥' from 'Comparison Type' and type '3' into 'Threshold' field.
This example can be seen on the following screen.

Then select option you wish to be used by clients and add it. Save the changes.
Important! Options selection is available only if a supported configurable options group has been enabled for the group of rules on its creation.

Note that only packages with selected products can be enabled!

Information about each hosting can be found here along with access to the hosting history.
Press 'View History' near desired hosting to view its history of changes.

As you can see, autoscaling is displayed on the main page of a product right below the Advanced Billing For WHMCS usage records.
Press 'Show' to view details.

To browse other options, use their names marked on the following screen.

Additionally, you can change the minimum interval between the changes through using marked field.

Do not forget to save changes when you finish.

For the settings shown on the following screen, notification will be sent once in ten minutes if the following rules are met.
The product number of Installed applications is equal or higher than 10.

• Product A: Max 4 FTP accounts and 500 MB storage.
• Product B: Max 10 FTP accounts and 1 GB storage.
• Product C: Max 20 FTP accounts and 5 GB storage.
  

Afterwards, you have created an autoscaling group, added products listed above to it and defined them with following rules.

• Product A - Lowest
  • Upgrade Rule: ≥ 3 FTP accounts & ≥ 400 MB storage
• Product B - Middle
  • Upgrade Rule: ≥ 9 FTP accounts & ≥ 8 GB storage
  • Downgrade Rule: ≤ 3 FTP accounts & ≤ 300 MB storage
• Product C - Highest
  • Downgrade Rule: ≤ 8 FTP accounts & ≤ 7 GB storage

1. A client, John orders product C and creates 3 FTP accounts in it.
2. Advanced Billing cron job changes product C to product B with the first run, and further to product A in the second run (if provided minimum time interval has passed).
3. John uploads 450 MB of files, so now his product meets product A top rule requirement.
4. Cron runs again, and changes his product to product B.
5. John creates additional 7 FTP accounts and uploads files with total size of 550 MB.
6. Now, his product meets product B upgrade rules only partially, therefore cron run does nothing.
7. Some time passes and total amount of storage used by John reaches 8 GB.
8. This time his product meets product B upgrade rules completely and is updated to product C.
9. John removes 4 of his FTP accounts and 1 GB of files.
10. Therefore his product meets product C bottom rules requirements and is downgraded to product B.

That was all about upgrading/downgrading the products, but let us now see how the payments look like.
If your client orders product C and their product gets downgraded to product B, they will be billed with product C price.
However, if the prices and free limits are set per resources, you will help your clients to avoid additional payments if their resource usage is low.
If you do it this way, clients will pay fixed price each month, but additional payment will depend on the resource they use.
In case you own only limited amount of resources, Product Auto Upgrade For WHMCS extension will allow you to use them more efficiently.
Whereas the core Advanced Billing For WHMCS features will let you bill your clients adequately.