My portable wd p/n wdbaau0010hbk-01 is not accepting another hdd inside

I wanted to upgrade my hdd inside my portable western digital external p/n wdbaau0010hbk-01 but it’s not reading any other hdd except the 1 which is already inside it…is there any compatibility problem?or is it programed for not accepting any other HDD ?
the new HDD is a western digital hard drive also and i’ve tried 3 other WD HDDs with different firmware version but nothing they all didn’t read on computer.