SSISDB restoring master key on a replica

Hi!

I am trying to add SSISDB to an availability group in an (Azure) 2016 always On configuration.

I have Added SSISDB to the AG and then attempted to execute a package via the SQL agent. This works on the primary node, but on the replica I get an error:

Please create a master key in the database or open the master key in the session before performing this operation.  

I then backed up the master key on the primary node:

backup master key to file = 'c:\temp\SSISDBKey'  
       encryption by password = 'password' 

Copied the key to the replica server and ran:

USE SSISDB
RESTORE MASTER KEY FROM FILE = 'c:\DBA\SSISDB\SSISDBKey'
DECRYPTION BY PASSWORD = 'Password'
ENCRYPTION BY PASSWORD = 'Password'

which gives me the message:

The old and new master keys are identical. No data re-encryption is required.

I then ran on the replica node

OPEN master Key decryption by password = 'Password' 
ALTER Master Key ADD encryption by Service Master Key

If I try to run the package at this point I get the error:

An error occurred during decryption.

Any idea what I'm doing wrong here? 

Thanks,

Zoe