Use api to create a new option in a question in nextcloud forms

Nextcloud's Form app has an API which allows the automatic creation of Forms/Questions/Options.I'm trying to create a new option for a question using this API: https://github.com/nextcloud/forms/blob/main/docs/API_v3.md#create-a-new-optionUsing this payload:

optionTexts": ["A new Option."]

Nextcloud always fails with this error:

OCA\Forms\Controller\ApiController::newOption(): Argument #3 ($optionTexts) must be of type array, null given, called in /snap/nextcloud/45124/htdocs/lib/private/AppFramework/Http/Dispatcher.php on line 208 in file '/var/snap/nextcloud/45124/nextcloud/extra-apps/forms/lib/Controller/ApiController.php' line 741

How can I set the correct type array?