Properly signing an extension.

Hi everyone,
We created an adobe HTML+JS+JSX panel and signed it with a self created certificate using the ZXPSignCmd tool, the extension used to work fine with all the 2018 versions of Adobe CC products. When our end user updated to 2019' versions, they where prompted with the invalid certificate error box and the extension didn't start correctly.
We planned to buy a certificate from a CA , but the link posted in the FAQ leads to the adobe exchange documentation and there's no list of approved partners.