Error: The text of your Tweet exceeds the number of allowed URLs.

Typefully isn't aware of the edge case where the content of a tweet exceeds the number of allowed URLs.
It seems like the maximum number of URLs you can have in a tweet is 10. One of the tweets in my thread had 11 URLs (all Twitter profile links). Typefully successfully posted the initial tweets in my thread, but when it got to the one with 11 URLs, it errored out and stopped posting. I had to manually delete all the tweets one by one on Twitter.