Hi there - I run evangelism at Backblaze; part of my role is to handle questions just like this. I didn’t notice this one earlier, since my Google alert is for backblaze, with only one l 
I’m guessing this is the same question I just answered over in our subreddit - it seems like there’s a bug in the S3 extension - it has an incorrect domain name suffix for Backblaze B2. I gave a workaround on the Reddit post, and posted a topic here explaining the bug before I saw this one.