Backup to Cloudian fails: "Backup failed for volume"

Hi Team,

I’m trying to take backup of sample Wordpress app. with PX-store PV to Cloudian(HW appliance/on-Prem Object Storage) , but fails with following error message.
I just selected a namespace as backup resources.

Backup failed for volume: cloudsnap Backup id: for d2ad2749-ea60-4121-8269-0422419efb25-wordpress-mysql-pvc did not succeed: [Failed to validate credentials: error validating credential: SerializationError: failed to unmarshal error message status code: 403, request id: , host id: caused by: UnmarshalError: failed to unmarshal error message 00000000 3c 68 74 6d 6c 3e 0d 0a 3c 68 65 61 64 3e 3c 74 |<html>..<head><t| 00000010 69 74 6c 65 3e 34 30 33 20 46 6f 72 62 69 64 64 |itle>403 Forbidd| 00000020 65 6e 3c 2f 74 69 74 6c 65 3e 3c 2f 68 65 61 64 |en</title></head| 00000030 3e 0d 0a 3c 62 6f 64 79 3e 0d 0a 3c 63 65 6e 74 |>..<body>..<cent| 00000040 65 72 3e 3c 68 31 3e 34 30 33 20 46 6f 72 62 69 |er><h1>403 Forbi| 00000050 64 64 65 6e 3c 2f 68 31 3e 3c 2f 63 65 6e 74 65 |dden</h1></cente| 00000060 72 3e 0d 0a 3c 68 72 3e 3c 63 65 6e 74 65 72 3e |r>..<hr><center>| 00000070 6f 70 65 6e 72 65 73 74 79 2f 31 2e 31 37 2e 38 |openresty/1.17.8| 00000080 2e 32 3c 2f 63 65 6e 74 65 72 3e 0d 0a 3c 2f 62 |.2</center>..</b| 00000090 6f 64 79 3e 0d 0a 3c 2f 68 74 6d 6c 3e 0d 0a |ody>..</html>..| caused by: expected element type <Error> but have <html> on Node-not-assigned]

What does the message mean?

When I tried to take backup to AWS S3 with selecting same namespace, the backup job was successfully completed.
Also, I tried to take backup to same Cloudian Storage with selecting same resources except PVs, the backup job was successfully completed.

I confirmed that validation of the backup location is passed.
(I’m disabling SSL because we don’t have an authorized certification.)

May I have any advices?
Regards