Unable to set--> serverless config credentials -p aws -k $key -s $secret (ssm issue)

I am trying to use ssm in my serverless.yml file, but when I try to run this command I am getting an error. Not sure if there is a work around? Below is my a snippit of my serverless.yml file where I am setting this in the environment section. Below that is what is happening when running serverless config.

ROUTING_NUMBERS_INFO: ${ssm:/bpf/default/products-api/ROUTING_NUMBERS_INFO}