There are limitations concerning the number of versions and aliases of app bundles and activities you can have:
https://forge.autodesk.com/en/docs/design-automation/v3/developers_guide/rate-limits/da-rate-limits/
At the time of writing this article the limit for both versions and aliases are 100 for all Design Automation services:
The easiest way to delete your oldest versions and aliases on a one-off basis is to use a utility like https://da-manager.autodesk.io/ or the Forge Visual Studio Code extension.
Once you did that you should be able to create new versions and aliases again.
Follow @AdamTheNagy Adam Nagy joined Autodesk back in 2005 and has been providing programming support, consulting, training and evangelism to external developers. He started his career in Budapest, then worked in Prague for 3 years and now lives in South England, UK. At the moment focusing on Inventor and Fusion 360, plus cloud and mobile related technologies. Adam has a degree in Software Engineering and has...