:help 'formatlistpat' says:

A pattern that is used to recognize a list header. This is used for the "n" flag in 'formatoptions'.

And :help 'formatoptions' says:

Vim default: "tcq"

:help fo-table describes the meaning of the n flag:

n        When formatting text, recognize numbered lists. This actually uses the 'formatlistpat' option, thus any kind of list can be used.
[..rest snipped..]

To add the flag, use:

set formatoptions+=n

:help 'formatlistpat' says:

A pattern that is used to recognize a list header. This is used for the "n" flag in 'formatoptions'.

And :help 'formatoptions' says:

Vim default: "tcq"

:help fo-table describes the meaning of the n flag:

n        When formatting text, recognize numbered lists. This actually uses the 'formatlistpat' option, thus any kind of list can be used.
[..rest snipped..]

So I suspect it's probably a matter of just adding this flag to formatoptions. To add the flag, use:

set formatoptions+=n