The request too large error is usually due to the request header larger than the buffer size. This shouldn’t happen unless if you have a firewall or proxy that inserts additional data to the header.
Yeah, for what it’s worth, I’ve run into this also, but it’s because I expose my OpenSprinkler web UI via Cloudflare Tunnels and put Cloudflare Access in front of it, so the world can’t see. CF Access drops a few authorization cookies (just shy of 1600 bytes) which get forwarded to the OpenSprinkler server, and it sounds like that’s too much for the buffer?
I ended up running an nginx proxy on the machine that runs my Cloudflare Tunnel to cut out the CF cookies before sending the requests to my OpenSprinkler controllers. If you’re increasing the buffer size to be able to handle this, that’d be convenient 🙂