I also confused because of below description result.
I understood that if there are same combination of two values, should return combination that distance between two values is shortest.

sum_pairs([10, 5, 2, 3, 7, 5],         10)
#              ^-----------^   5 + 5 = 10, indices: 1, 5
#                    ^--^      3 + 7 = 10, indices: 3, 4 *
#  * entire pair is earlier, and therefore is the correct answer
== [3, 7]

If that, what is the below case's expected answer?

sum_pairs([10, 5, 2, 5, 3, 7, 5],         10)

Through my understanding, the expected combination is '[3, 7]'.
If I was wrong, I am sorry confusing everyone.

sum_pairs([10, 5, 2, 5, 3, 7, 5],         10)
               ^-----^          5 + 5 = 10, indices: 1, 3
                        ^--^    3 + 7 = 10, indices: 4, 5 *

The one requirement is absent.
'the definition of valid spacing is one space between words'