Verse 3

3.  The lack of chariots and others seen in dream is shown in the Upanishads along with the soul's entering and going out of Maya,  (the dream and waking states),  they speak of the unreality as indeed proved by that statement,  as being evident in dream.

"The lack of chariots and others seen in dream is shown in the Upanishads"

Here the Brihadaranyaka Upanishad is cited as confirming that a dream is a conscious "state",  as it were,  furnished with objects lit by the intellect of the dreaming one alone,  that is,  lacking material reality.
Reference  :-
"There are no chariots....but he creates the chariots"  Brihadaranyaka Upanishad 4.3.10

"along with the soul's entering and going out of Maya,  (the dream and waking states)"

Therefore,  due to the fact that whatever is being perceived,  that very perception itself is taking place within an unreal  "state".
The meaning is,  entities perceived within a dream state are accepted as being unreal due to the dream state itself being known later,  from memory,  as being unreal.
Just the same,  Gaudapada is saying,  the  "waking state"  is also a transitory delusional state.  We have had this demonstrated for us by the Mandukya Upanishad.
Therefore,  all entities experienced in the  "waking state"  are also unreal due to there being also perceived from a  "state within".

"they speak of the unreality as indeed proved by that statement,  as being evident in dream".

This refers to the above statement by the Brihadaranyaka Upanishad,  which said that in a dream containing chariots the chariots were not there to start with,  they were imagined or created by the dreaming self or jiva  (limited  "state"  within consciousness).  All of which are subject to changes of state,  such as waking and dreaming,  which are known to be delusions and unreal.