The errors you see on the debug log are responses returned by your server. You should be seeing error 413s being recorded as most web servers are not configured to handle request bodies with sizes >1MB. The solution here would be to increase the size limit on POST requests on your web server or proxy, for example:

If you are using Nginx, navigate to the configuration directory and create/edit the configuration, setting client_max_body_size to 50MB (just in case).

This is typical practice, especially for sending large files over http. And whilst Terra does chunk payloads, they are chunked by days if the request spans over weeks.