Hi @Arunachalam J,
Thank you for posting in this community.
1.Make sure you are an administrator of SharePoint farm. Disable and then re-enable the App Installation Service via Central Administration > Monitoring > Review job definitions > App Installation Service. Retry uploading the SPPKG packages to see if the problem persists.
2.Please upload the SPPKG packages on another computer using another SharePoint farm administrator account to see if the problem persists.
3.Please try adding the SPPKG packages to another App Catalog Site to see if the problem persists.
4.You can try to use this method in this thread: 'Refused to connect' error when trying to add app in SharePoint 2019.
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