When entering a wireguard config via the wireguard client panel, if you upload an IPv6 config, it's fine. However, if you chose manual input, or try to edit an existing one, and it uses IPv6, it fails.
This occurs specifically if it has a set of characters in it.
Here is an example working and bad config - these are mullvad Hong Kong servers, with a key I generated not associated with a real mullvad account, that can reproduce the issue. The error that is returned is "Illegal parameter, operation failed. [-32602]"
Removing the [] in the endpoint makes this work, so it seems to be a validation issue. Uploading this from a .conf file works flawlessly, and the VPN connects successfully (with a key that is actually valid - as siad, the below key doesn't map to any account)
[Interface]
PrivateKey = wFwRbub338uy8rRsSiNgCRbz1uz39u7/c1dEjGDAx2U=
Address = 10.68.92.62/32,fc00:bbbb:bbbb:bb01::5:5c3d/128
DNS = 10.64.0.1
[Peer]
PublicKey = zmhMPHfkgo+uQxP+l919Gw7cj5NTatg9nMU37eEUWis=
AllowedIPs = 0.0.0.0/0,::0/0
Endpoint = [2403:2c81:1000::a05f]:51820
Panel version: v4.7.13
Model: GL.iNet GL-BE9300
OpenWrt Version: OpenWrt 23.05-SNAPSHOT
Kernel Version: 5.4.213