This HN comment[1] enlightened me.
1: https://news.ycombinator.com/item?id=9447636
---
To download a file:
curl -u david:$(op item get flounder --fields label=password) \
-O sftp://flounder.online:2024/index.gmi
To upload a file:
curl -u david:$(op item get flounder --fields label=password) \
sftp://flounder.online:2024 --upload-file index.gmi
/posts/