How to get the bottom level taxonomy on a post page?

Question

WordPress

category>1category
I need to get 1 category on a post page.
Tried through get_the_terms( get_the_id(), 'category )[1]->term_taxonomy_id;
But on some pages it is at index 0.

Answer 1

php.net/manual/en/function.array-reverse.php

$terms = get_the_terms( get_the_id(), 'category' );
$terms = array_reverse( $terms );
echo $terms[0]->term_taxonomy_id;