Hello @MS Techie - I have confirmed with our Product Group that, as of this writing, the HTTP + Swagger Action is yet to support OpenAPI V3 spec.
When a v2 spec is provided to the prompt, the Action is working as expected. While the team prioritizes the work of supporting v3 spec, if you feel that we should communicate this detail better via our docs, please consider opening a new issue under the documentation by using the "This page" button found at the bottom of page: HTTP + Swagger doc.
I hope this info brings clarity to the issue observed above and helps with the planning of your project.