It sounds like the existing version of the app is set to 1234. When building the Android app, manually override the version number and make the version code higher than 1234.
![override_version.png override_version.png](/t5/image/serverpage/image-id/5283i62D7CEB1818F593E/image-size/large?v=v2&px=999)
Then download the app, sign it, and submit it to Google Play, and it should go through.