Is there an alternative to the Sketchup Encryption service?

I’d like to encrypt my extension. But I’m unable to encrypt my extension using the service at Sign Extension | SketchUp Extension Warehouse
It throws me the following error.

Assuming there were issues with my extension, I tried doing it with a single ruby extension file. That is also ending up with the same error. Tried different extensions that I have encrypted before but in vain.

Is there a bug in the service that others are facing?
Is there any alternative service or product that I can use as a fallback so that I don’t need to depend on Sketchup?

Your RBZ [a renamed ZIP archive] needs to contain two things.
An RB ‘loader’ and a subfolder of the exact same name.
Nothing else is expected.
The subfolder can be empty as it’s where the signing file is put, but any RB files [typically the larger ‘code’ file[s]] in the subfolder will be encrypted into the RBE format if you choose to do that.

@TIG is right that the most likely cause of your problem is that your rbz is not organized the way the SketchUp encrypter expects.

SketchUp only knows how to load encrypted files created with its own proprietary encryption system, so any direct alternative would require violation of the TOS prohibition against reverse engineering SketchUp. You could roll your own, but of course you would have to come up with a way to decrypt your own proprietary coding and then load the plain text Ruby code. But unless your proprietary scheme is itself uncrackable, you are back to square one.