How to upload a base64 encoded image for a Gitlab issue?

Question

GitLab

Good afternoon,
I have a Mantis bug tracker and a project on Gitlab. In the mantis, people create tasks (issues), which are then collected by cron and imported into Gitlab.
Everything works fine except for uploading attachments from mantis to gitlab.
I read in the gitlab documentation that they have a POST method for uploading images
` https://docs.gitlab.com/ce/api/projects.html#uploa...
However, in their example they indicate that the file should be already loaded into the file system. The question is - can I send a base64 encoded file to gitlab with cURL, or do I still need to send a file that is already physically on disk? Perhaps someone faced such a problem?