Unsupported header 'x-amz-checksum-crc32' received for this API call.

For some time after February 2025 and before November 2025, Discourse updates and backups to Backblaze failed due to an unsupported header x-amz-checksum-crc32. For example: ¹

I, [2025-04-02T08:51:34.524786 #1]  INFO -- : > cd /var/www/discourse && sudo -E -u discourse bundle exec rake s3:upload_assets
`/root` is not writable.
Bundler will use `/tmp/bundler20250402-1714-yuyf6i1714' as your home directory temporarily.
rake aborted!
Aws::S3::Errors::InvalidArgument: Unsupported header 'x-amz-checksum-crc32' received for this API call. (Aws::S3::Errors::InvalidArgument)

This was because of a breaking change in the AWS SDK that had been reported, but was closed as "not planned". There was a workaround ², but this workaround stopped working sometime in 2026 due to some changes in the Discourse codebase. ³

In the case of Backblaze, a workaround is no longer necessary because they updated their API to work with the new headers sometime before November 2025. ³