Nextcloud IOS App LAN address http error

New forum user here.

I have a fine nextcloud sitting behind a nginx reverse proxy with https rewrite and letsencrypt installed to deal with any public internet http/https connection. Nextcloud is running on another VM with centos7+apache without any SSL mechanism.

Internally, I have a DNS server to resolve nextcloud as an internal 172.16.x.x and so that all browser/desktop apps can access to nextcloud directly without going through nginx.

The question I would like to ask is on the IOS nextcloud APP.

I have setup the account in the app when I am on the street, server name is http://nextcloud.domain.tld. Once granted access, I can see that the server name on the app changes to https://nextcloud.domain.tld. This is fine when I use it externally, photos sync etc.

However, if I am on LAN with my phone, https is not a valid connection since the nextcloud apache is not listening 443.

The sad thing is that, I can use my iPhone safari to access http://nextcloud.domain.tld internally, but if I remove the account on the mobile app, and set it up again with the url http://nextcloud.domain.tld, the app prompts SSL error?

Is this a bug on the app, or it blocks http on purpose?