This is a placeholder entry.
There is no API endpoint "project" in translate5. Projects are just tasks with a special taskType. See Task#Tasktypes.
To create a project, create a task and assign multiple target languages to it. For more information, how this works under the hood, see Task#Tasktypes
Example of how to create Project with curl
curl --location --request POST 'http://your-domain.com/editor/task' \ --header 'Translate5AuthToken: YOUR_AUTH_TOKEN' \ --form 'customerId="1"' \ --form 'taskName="Test task name"' \ --form 'enableSourceEditing="0"' \ --form 'edit100PercentMatch="1"' \ --form 'lockLocked="1"' \ --form 'mappingType="source"' \ --form 'sourceLang="361"' \ --form 'targetLang[]="251"' \ --form 'targetLang[]="252"' \ --form 'autoStartImport="1"' \ --form 'importUpload[]=@"/path/to/file/1-seg-3.xlf"' \ --form 'importUpload_language[]="251"' \ --form 'importUpload_language[]="252"' \ --form 'importUpload_type[]="workfiles"' \ --form 'taskType="project"'