Can't publish on Amazon App Store

I've been trying to update my apps on Amazon App Store for more than a year now, and the main APKs are just not uploading and I receive an 'Invalid Input' error message without further explanation.

Contacting Amazon to solve this has turned into a waste of time as they either not reply at all, or simply provide useless information, asking me to check version name and code in the APK and its signature, repeatedly. FWIW I verified that signature doesn't matter as their portal change it automatically and version name/code, if they had done their home work, is very easy to verify.

Last actual reply I received is dated back in July 27th 2020 and it said: " This issue has been escalated and the submissions team is investigating. I do not have an ETA at the moment, however we will respond as soon as there are any updates. We appreciate your understanding in this matter. Thanks! "

Since, I've asked for an update on this case and received no reply whatsoever!