CodeMagic Error "Failed Step: Fetch signing files" after apple developer account expired.

It's be several months since I worked on my app.

In that time, my developer account expired. Also, I haven't updated to the latest Flutterflow yet.

I got the following error when I tried to submit a new build.

Failed Step: Fetch signing files
...
--private-key: Provided value is not a valid PEM encoded private key.
Build failed 
Step 4 script 'Fetch signing files' exited with status code 2

I've renewed my apple account and signed the new apple agreements. Do I need to wait a while? Do I need to create a new private key? Do I need to update to the latest Flutterflow (which will probably break some custom modules?)