Hello David, thank you for submitting a question. Our Office Add-ins documentation has an article section that describes deploying updates to your add-in: https://learn.microsoft.com/en-us/office/dev/add-ins/publish/maintain-breaking-changes#deploy-updates
If you've updated the manifest, the article includes the following note:
Whenever you make a change to the manifest, you must raise the version number of the manifest.
Have you tried raising the version number of the manifest?