Invalid Security Token *only* when using Transcribe

I am using Vapor to deploy my laravel application to AWS. The keys that I am using locally to connect to AWS Transcribe are working, but I am getting this error when I send a request to Transcribe from one of my Vapor environments:

{"__type":"UnrecognizedClientException","message":"The security token included in the request is invalid."}

I am using my environment variables AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY to authenticate in multiple places (including my Transcribe request) but this is the only failure. Again, this works fine locally. I have also opened a ticket with Vapor so they may have a solution for me soon - but my gut tells me this needs to be solved from within my AWS console.

Any suggestions are appreciated! Thanks in advance.