When working with the c4 tool or the aws command line interface you may receive a message that your security token is not valid anymore. The easiest fix for this is to issue the following to commands:
rm ~/.aws/credentials
aws configure
You should be able to use the aws cli and c4 tool again.
In case you have enabled Multi-Factor-Authentication (MFA), the aws command line interface will ask you to provide a one-time security token from time-to-time, generated by the Authenticator application of your choice when you activated MFA.
If the problems persist, try executing your aws command with the following parameter:
aws <commands> <parameters> --profile default-mfa
The name of the profile can be identified with
less ~/.aws/credentials
IF AWS is complaining about a missing token, you can requets a new token with
c4 aws token -f
Have your authenticator device / app ready.