feat: add initial PPE documentation (#1256)

Co-authored-by: Michał Olender <[email protected]>

Author: mhamas

sources/platform/actors/running/images/store/pay_per_event_example_actor.png

@@ -20,19 +20,21 @@ Anyone is welcome to [publish Actors](/platform/actors/publishing) in the store,
 
 ## Pricing models
 
-All Actors in [Apify Store](https://apify.com/store) fall into one of the three pricing models:
+[//]: # (TODO: link platform usage docs)
+All Actors in [Apify Store](https://apify.com/store) fall into one of the four pricing models:
 
 1. [**Rental**](#rental-actors) - to continue using the Actor after the trial period, you must rent the Actor from the developer and pay a flat monthly fee in addition to the costs associated with the platform usage that the Actor generates.
 2. [**Pay per result**](#pay-per-result) - you do not pay for platform usage the Actor generates and instead just pay for the results it produces.
-3. [**Pay per usage**](#pay-per-usage) - you can run the Actor and you pay for the platform usage the Actor generates.
+3. [**Pay per event**](#pay-per-event) - you can run the Actor and you do not pay for platform usage the Actor generates. Instead you pay for the specific events the Actor creator defines, such as for generating a single result or starting the Actor.
+4. [**Pay per usage**](#pay-per-usage) - you can run the Actor and you pay for the platform usage the Actor generates.
 
 ### Rental Actors
 
 Rental Actors are Actors for which you have to pay a recurring fee to the developer after your trial period ends. This empowers the developer to dedicate more time and effort to their Actors, thus ensuring they are of the _highest quality_ and receive _ongoing maintenance_.
 
 ![Rental Actor example](./images/store/rental-actor-example.png)
 
-Each rental Actor has a _free trial_ period. The length of the trial is displayed on each Actor's page.
+Most rental Actors have a _free trial_ period. The length of the trial is displayed on each Actor's page.
 
 ![Rental Actors in Apify Store](./images/store/rental-actor-trial-example.png)
 
@@ -47,6 +49,7 @@ Yes, when you are renting an Actor, you can run it using either our [API](/api/v
 
 ##### Do I pay platform costs for running rental Actors?
 
+[//]: # (TODO better link for platform usage costs explaining what it is!)
 Yes, you will pay normal [platform usage costs](https://apify.com/pricing) on top of the monthly Actor rental fee. The platform costs work exactly the same way as for free public Actors or your private Actors. You should find estimates of the cost of usage in each individual rental Actor's README ([see an example](https://apify.com/compass/crawler-google-places#how-much-will-it-cost)).
 
 ##### Do I need an Apify paid plan to use rental Actors?
@@ -138,6 +141,52 @@ at the bottom of the [Usage tab](https://console.apify.com/billing).
 
 ![Actor pay-per-result cost](./images/store/pay_per_result_actor_items.png)
 
+### Pay per event
+
+Pay per event Actor pricing model is very similar to the pay per result model. You still do not pay the underlying platform usage. Instead of results, you pay for specific events defined by the creator of the Actor. These events will vary between Actors, and will always be described, together with their pricing, on each Actor. Example events might be producing a single result, doing a unit piece of work (e.g. uploading a file) or starting an Actor.
+
+#### Pay per event Actors - Frequently Asked Questions
+
+#### How do I know Actor is paid per events?
+
+You will the that the Actor is paid per events next to the Actor name.
+
+[//]: # (TODO: also show the screenshot from Apify Store on Web)
+
+![Example pay per event Actor](./images/store/pay_per_event_example_actor.png)
+
+#### Do I need to pay a monthly rental fee to run the Actor?
+
+No, you only pay for the events.
+
+#### What happens when I interact with the dataset after the run finishes?
+
+You would still pay for all interactions after the Actor run finishes, same as for pay per result Actors.
+
+#### Do I pay for the storage of results on the Apify platform?
+
+You would still pay for the long term storage of results, same as for pay per result Actors.
+
+#### Where do I see how much I was charged for the pay per result Actors?
+
+Similarly to pay per result Actors, you can see how much you have been charged on your invoices, and on the [Usage tab](https://console.apify.com/billing) of the Billing section in the Console.
+
+![Pay per event Actor - historical usage tab](./images/store/pay_per_event_historical_usage_tab.png)
+
+You can also see the cost of each run on the run detail itself.
+
+![Pay per event Actor - run detail](./images/store/pay_per_event_price_on_run_detail.png)
+
+#### Can I put a cap on a cost of a single Actor run?
+
+Yes, when starting an Actor run, you can define the maximum limit on the cost of that run. When the Actor reaches the defined limit, it should terminate gracefully. Even if it didn't, for any reason, and kept producing results, we make always sure you are never charged more that your defined limit.
+
+![Pay per event Actor - max charge per run](./images/store/pay_per_event_price_on_run_detail.png)
+
+#### How do I raise a dispute if the charges for an Actor seem off?
+
+Please, in such a case, do not hesitate to contact the Actor author or our support team. If you suspect a bug in the Actor, you can also always create an issue on the Actor detail in the Apify Console.
+
 ### Pay per usage
 
 When you use a pay per usage Actor, you are only charged for the platform usage that the runs of this Actor generate. [Platform usage](./usage_and_resources.md) includes components such as compute units, operations on [storages](/platform/storage), and usage of [residential proxies](/platform/proxy/residential-proxy) or [SERPs](/platform/proxy/google-serp-proxy).