I know what the error means lmao. Also, like I said, the directions and deliverables were not specified, next time maybe just try a bit harder when putting the kata together.

I tested your code by adding echo($n); before $a = [];.
In its random test, for example n=261, the error message started by the following message.

Failed asserting that two arrays are equal.
Expected: Array (
    0 => '162'
    1 => '062'
    ...

By scrolling down, I also saw the following message that should be the expected data.

Actual  : Array (
    0 => 261
    1 => 260

If you see the first sample test, it says that the output from reverseSeq(5) is expected as [5,4,3,2,1]. So return type should be clear.

About the error you had, when I googled the syntax error message, the following page was found.

https://stackoverflow.com/questions/30971253/php-unexpected-array-t-array