How Do I Use S3 Object Storage In My Code?

Please note that due to it’s complexity Contabo does not offer any support for coding / programming issues.

The following information is not a step-by-step guide, but a few suggestions on setting this up.

The S3 Object Storage API was defined by Amazon AWS more than 10 years ago and is maintained by them. Please see https://docs.aws.amazon.com/AmazonS3/latest/API/Welcome.html.
Not all Amazon S3 features are supported. Please see https://docs.ceph.com/en/latest/radosgw/s3/.
The API documented at https://api.contabo.com/#tag/Object-Storages is not the S3 Object Storage API. It is mainly for purchasing and increasing storage size. For uploading/downloading files and folders and managing buckets, please use the S3 Object Storage API.
In general, it is not recommended to make the S3 Object Storage API calls directly, e.g. via curl. Because the S3 API is based on HMAC please use the S3 SDK libraries that are available for many programming languages. Please see
https://aws.amazon.com/developer/tools/ or perform an internet search for alternatives.

Here are some examples where the integration was made:

cntb written in Go and using the minio library.
External article on dev.to using NodeJS and Python.
External repository by lucafulgenzi using SpringBoot.
Ceph Object Gateway docs include examples for C++, C#, Java, Perl, PHP, Python and Ruby.