The Era 2 have a total of 4 2.5" mounts, but 2 of these can only be used in spine setting 1 and 2.
The first 2 have a dedicated bracket in the left chamber by the front:
They sit in a rail going outwards in the case, so when 2.5" SSDs are installed, you slide it back in and secure the screw:
The second position for the other 2 is on the internal spine next to the power supply area:
Due to the tight space here, SSDs will only fit in spine position 1 and 2, and the max thickness for position 1 is 16 mm, while position 2 offer 9 mm thickness.