S3 dynamic date prefix in folder name by using current date as backup_add_prefix

So what i want to do is use Logstash to rename incoming files in a s3 bucket.

I run it via docker and use the following logstash.conf

input {
s3 {
access_key_id => "some_key"
secret_access_key => "some_secret"
region => "some_region"
bucket => "mybucket"
interval => "10"
sincedb_path => "/tmp/sincedb_something"
backup_add_prefix =>'%{+YYYY.MM.dd}/'
backup_to_bucket => "mybucket"
additional_settings => {
force_path_style => true
follow_redirects => false

Basically i want backup_add_prefix =>'%{+YYYY.MM.dd}/' to be the current date, so that logstash builds a structure where incoming files a put into date folders.
The syntax does not work though. Is there a way to make backup_add_prefix a changing date?

No, the code uses string interpolation to prefix the name. It does not sprintf it.