Via the interface

Check that your book is online

In the Publications tab, the tick in the publication's record is green.

Then, you can go to the Market section and check the availability of your publication in each of your activated sales outlets.

Do not change the current price

Go to Metadata > Sales. The current price is the price with the green background colour.

You do not need to make any changes to the current price. When the promotion ends, this price will automatically be applied again.

Add the promotional price

Still in the Sales > Sales prices section, click on Add.
Select the currency (this will select the countries covered by this currency, and therefore by the promotion).
Enter the desired amount (preferably choosing prices ending in .99).
In the Starts on field, document the date on which the promotion should start.*
In the Ends on field, document the date on which the promotion should end.*
Click on Save.

* The dates are inclusive, over the whole day (from 00:00 to 23:59).

Thus, in the Metadata/Sales section, on the Price tab, you will see a line with a green background colour (active price) and a line with a blue background colour (future promotional price).

Example :

For this example, the promotion starts on 25-08-2022 and ends on 23-09-2022 inclusive. On September 24 at midnight, the platform automatically reapplies the current price of $9.99.