Solution:
The error occurs because the _x() function requires two parameters:
1. The text string to translate.
2. Context information for translators.
If you don’t need to provide context, you should use the __() function instead.
And if you don’t need translation at all, just use plain strings.
For example, both of these are valid:
'label' => __('Recipes'),
'singular_label' => __('Recipe'),
Or, without translation:
'label' => 'Recipes',
'singular_label' => 'Recipe',
👉 Use _x() only when you want to supply translator context. Otherwise, stick with __() or plain text.