AWS Error "No AWSAccessKey" when trying to upload HTML or ZIP Assets to PDF Serives Internal Storage

I am trying to convert a local html file to PDF through Adobe PDF Services' REST API.

I have followed the steps at https://developer.adobe.com/document-services/docs/overview/pdf-services-api/gettingstarted/

But  I get stuck on Step 2 Section 2: Uploading the Asset, with an error from AWS: "No AWSAccessKey was presented."

I can successfully retrieve the "uploadUri" with:

curl -H "Authorization: Bearer {{ access_token }}" \
-H "X-api-key: {{ client_id }}" \
-H "Content-Type: application/json" \
-d "{\"mediaType\": \"application/zip\"}" \
-X POST https://pdf-services-ue1.adobe.io/assets 

But the following command always returns an error from AWS (see "aws_error.txt" attached)

curl --location -g --request PUT  {{ uploadUri }} \
-H "Content-Type: application/zip" \
--data-binary @8998938.zip

 I have also tried it setting the "mediaType" and "Content-Type" to "text/html" and using "--data-binary @8998938.html". The response was the same.

Any help would be greatly appreciated,

Kane