Hello Carolyn Schroeder,
Thanks for your question.
It is possible your certificate in AKV was imported as pem and not as pcks12. Re-import the cert from a pfx file with the --password parameter.
az keyvault certificate import --password $password
Also see similar issue here from stackoverflow for an alternative solution: https://stackoverflow.com/questions/65781652/error-the-parameter-keyvaultcsmid-has-an-invalid-value-while-adding-app-servic
You can mark it 'Accept Answer' and 'Upvote' if this helped you
Regards,
Abiola