Return unique values across multiple sheets – google sheets

I have multiple sheets that are named by month.
Each sheet has a section where it gets all unique values in a range by using =UNIQUE(the_range) which is what I want.

I want to create a summary sheet which then pulls all the unique values from all the sheet within a defined range. Currently I’ve tried this:

=UNIQUE({'01 July - 12 July 2021'!G10:G22,'June 2021'!G10:G22,'May 2021'!G11:G19,'April 2021'!G10:G20}, false, false)

The error returned is: Function array_row parameter 3 has mismatched row size

Can anyone help me find a better way to return these unique values across multiple sheets?

Thanks