# Developers

This is a (perpetual) work in progress so please mention if something feels out of date!

### Hive Transactions

Below is the documentation for various blockchain payloads that Splinterlands processes and what their payload means.

#### sm\_update\_rental\_price

This call is used to update the price of all the cards currently listed on the market, or rented out. Rented out cards are automatically cancelled and their price is updated to the price specified when they are relisted on the market when the card is cancelled during the next rental payment processing. The payload in the custom JSON field is of the following type (remember that the field must be a stringified version of this payload):

```typescript
type payload = {
    items: [string, number][], // [['<market_id>', <new_price>]]
    player?: string,           // '<username>'
};
```

Where:

* `items` is an array of tuples which contain the `market_id` of the item you wish to update and the new price you wish to set for that item.
* `player` is an optional field, which you can set to the name of another player if that player has given you rental authority.