iOs shared secret - BDK in-App purchases

Hey there. I am using BDK and want to set up in-App purchases in my native App trying to follow this guide of BDK.
Currently due my test phase there is an error in the backend API workflow, because BDK can’t get acces to the iOs receipt data. I think it is because of a false in-App shared secret from iOs. I’m not really sure which input has to come in the field of the BDK plugin in Bubble:

I’ve already created an app-specific in-app shared iOs secret. Could you please tell me rather this must come in the BDK plugin input:

Or this (code of the .p8 file):

Or this:

Thanks in advance and best regards.