Cannot build packages for Leap 15.3 on ARMv7

Recently I tried to configure OBS to build a binary package for Cubietruck SBC runing openSUSE Leap 15.3. By default, the 15.3 has configured the repository path containing openSUSE:Leap:15.3/standard. Since there is no arm7l architecture enabled for standard, the package status is unresolvable. If I add (or change to) the repository path openSUSE:Leap:15.3/ports, I get nothing more, the build is still in unresolvable state and a red triangle with white excamation mark show up in repository status. Is something misconfigured in OBS? Or am I doing something wrong?