Does your bucket have object lock enabled?

Yes

This could be the problem. Backup jobs can't create immutable backups on object lock enabled buckets. You can only storage backup copies on such object storage.

Can you create an additional bucket which doesn't have object lock enabled and try to use this one in your backup job?

Ah okay, i am not sure that is possible with BackBlaze according to this page:
https://www.veeam.com/sys238

You should be able to create buckets without object lock. The article you posted is about VBR but if you scroll down to the red box, there's a screenshot from backblaze which shows the object lock option.

When i try to use a bucket that has object lock disabled i get this message:
 

Can you go into the backblaze portal, find your bucket, open its lifecycle settings, and share a picture of that please?

Also, I found this which suggests versioning might not be possible to disable for backblaze:

https://forums.veeam.com/object-storage-f52/error-creating-b2-object-repository-t70196.html

You should be able to create buckets without object lock. The article you posted is about VBR but if you scroll down to the red box, there's a screenshot from backblaze which shows the object lock option.

When i try to use a bucket that has object lock disabled i get this message:
 

 

You can bypass this with VBR but VB365 you cannot unfortunately.

Both buckets show this:

Thanks for this. There’s nothing here to suggest completely disabling the versioning feature. I’d suggest you raise a case with Backblaze to see if that can be disabled. Otherwise you’ll need to enable object lock again and use backblaze as a backup copy destination only

Will “Keep only the last version of the file” disable versioning?

It seems to be possible to use Backblaze as a primary target for backup jobs. So there maybe something we overlook.

Thank you for the suggestion, just tried that and still got the error. Looks like ill either need to ask backblaze if versioning can be disabled or use another cloud backup solution for primary.

I’ve run into this in the past as well, but since I was using Wasabi, I was able to have versioning/object locking disabled. 

Please report back what you find out….B2 was one of the other vendors I had looked at and I’d be curious of object locking is a requirement for them.

Spoke with B2 support and it seems to be they were unaware it didn’t work, they first linked me to a docs page to create the storage object/repo but after i explained it didn’t work they came back to me about 30 mins later with this: