I'm using Migration API to migrate a huge number of documents to Prismic. At some point I get response 429 from Prismic but it looks like that the documents are being created anyway. How's that possible? Which are the limitations of the Migration API?
I also have one more question: is there a way to bulk publish all the documents in the migration release once the 1000 documents in the migration release is reached?
I've tried the migration release.
Once you've uploaded, you can bulk publish them.
It shows a progress indicator when you hit publish, and doesn't take that long.
As @aadtyaraj01 mentioned (thanks 
), you can bulk publish up to 1k documents via the Migration Release screen.
429s can occur if the rate limit (currently 1 request/second) is exceeded. For the 429 errors, generally these should result in the document not being created - it's interesting that you are seeing documents be created despite it, it would be great if you could report this to us in case you experience it again and mention the timestamp and the document id (if making a PUT request).