Publishing certificate question

I was trying to update an app that I published on the Play Store a long time ago. But, when I tried to upload the latest .apk file, it gave me this error. I don't know what to do about it?

Play Store signing issues are discussed here .

There are several that seem to discuss your issue. Perhaps APK signing with Google Play

Good luck.

@Steven_Rice I had the same problem and here is the solution Problem with signing app
You need to generate a new signing key with standard user=android, password=android etc. Send it to AI2 and generate new PEM file from your key. Everything is described on forum. And the new PEM send to google.