Yep, that does seem to be the problem. Can’t create a project and immediately start uploading and annotating from the API, despite the project creation endpoint returning success.
First test, I created a new project (happens when a user registers for my app), then annotated a few images, press ‘finished’, which uploads the images, and uploads the annotation for each image after it uploads successfully. The images uploaded, but annotations failed to upload.
Tried it again after a few minutes with that same project, images and annotations uploaded no problem.