Correct spelling, explanation: indisputable is a pretty complex word consisting of a prefix in-, the base word dispute, and then the suffix -able. Technically, without any changes, the word would look like in-dispute-able, but in the case of the ea cluster, the spelling is generally adjusted to leave only a, hence indisputable is the correct spelling.

Definition of indisputable:
adjective
1. unquestionable, not to be discussed
Usain Bolt is an indisputable icon among sprinters.
The evidence was indisputable and the attacker was found guilty.

Incorrect spelling, explanation: indisputable is constructed by using the suffix -able, which does, in fact, have the variant -ible in some cases. It’s used in the word possible, for example, because here poss is not an independent word, the same with edible. Indisputible is incorrect, however, because it’s a compound of suffixes and the base word dispute which functions independently.