hello @SanjeevSoni
can you please check the following:
1. in the Power Automate web portal, go to Data > Gateway and see if your gateway is listed there
2. on the gateway list page: hit the ... menu for the gateway you want to use > click Details > read in which region your gateway is currently deployed
3. check that your environment in Power Platform is deployed in the same region as your gateway: click on the wheel in the top right corner of your screen near the picture > click on Admin Center > click on Environments > click on the environment name in the list view > read details of what region it's in
If they don't match, then this is the reason. To fix things, uninstall your gateway and reinstall it in the right region.
Hope this helps! let us know if it doesn't so we can assist further. If it does, feel free to mark this answer as the solution!
Happy Automation,
Amina