Release apk from google play and manual installation?

Question

Android

The situation is as follows:
I have an application that is published on google play (version code: 100, version name 1.100). Also I want to add a feature that allows people to update the application using the apk (release) from the site (manual installation).
BUT during testing, I found the following problem:
After downloading the app from the store (v - 100), I try to install (update) using the created apk, and the result is "App not installed". But if I use the same apk (manually install) that was published to store and install the new version, everything works fine.
Can you describe if there are any restrictions on additional checks for security, or is there something wrong on my part?
ps all about release version - signed with the same key

Answer 1

When publishing, Google suggests using your signature. Perhaps, on the GP applications with Google, and on the site with the native one - that's the conflict?