Curl -4 instead of curl -6 to bitcoin RPC?

I’m bumping into an issue where I need to use IPV4 to RPC my Bitcoin node (umbrel RPi), instead of the usual IPV6. I’m not a networking guy so I might be asking for the wrong thing. But here’s where I am so far…

With the following command:

curl -d '{"jsonrpc":"1.0","id":"homeassistant","method":"getblockcount","params":[]}' -u "umbrel:PASSWORD" -6 "http://umbrel.local:8332/" -v

… I receive the correct JSON response from Bitcoin RPC (from my desktop Terminal). However when using:

curl -d '{"jsonrpc":"1.0","id":"homeassistant","method":"getblockcount","params":[]}' -u "umbrel:PASSWORD" -4 "http://umbrel.local:8332/" -v 

I get the following error:

< HTTP/1.1 403 Forbidden
< Date: Sun, 25 Feb 2024 11:46:24 GMT
< Content-Length: 0
< Content-Type: text/html; charset=ISO-8859-1

Are there settings I can change on the RPi umbrel node to allow IPV4? Or am I barking up the wrong tree?! Thanks.