After trying to install another extension, a problem occurred with your stamps extension. After some inquiries a conclusion presented itself and I quote our server-side, magento specialized support:
“It is the ExtensionHawk Stamps extension. It is using an Magento 1 class for some odd reason and this is a Magento 2 site, it is definitely a code issue with that extension that the extension developers will need to sort out.”
Please reach out if we can provide further information and also what to do next.
We assure you that we will resolve all your outstanding issues.
However, to check it,we require access to your website so that we can check the exact problem and correct the code (if any change is required).
Or else if you can direct us to the exact problem, that would be also fine for us.
Request you to reply us via ticket so that we can quickly resolve your case.