Google Cloud does not like my Customer-supplied encryption key (CSEK)

I'm trying to encrypt a VM image with my own provided key. So I go to my Terminal emulator and do:

$ openssl enc -aes256 -A -P                    
enter aes-256-cbc encryption password:
Verifying - enter aes-256-cbc encryption password:
salt=DCD571B7A0EC122B
key=786D832EBF415B5F6BCF852AC8DC38826D904DEAFC53885F3B9F49003788B073
iv =B641A744631C462ED2896563F2AB9A1C

I punch in the key into Google cloud and it throws back an error: So I read the documentation from Google about CSEK and it reads: So I run that script, I get the results in base64, but then it doesn't accept it (however, it does accept the one from the Google example). Do I have to pass this resulting base64 string to openssl enc? I'm a bit lost, and Google doesn't provide any results that apply to my case. Any help and/or guidance would be greatly appreciated!