BGP peer was configured , and as per BGP rules of advertising , 1) we need static route or 2) ip address on physical interface to advertise the routes to neighbor,
we used static routes but as customer divided their network in smaller subnets like /26 or /28 (for example :X.X.240.0/24 was divided in X.X.240.0/26 and X.X.240.64/26)
we used static route for these smaller subnets to advertise the , (example : ip route-static X.X.240.0 26 Null 0 , and ip route-static XX.240.64 26 Null 0 ,
we were not able to advertise the routes to our neighbor ISP router. so the internal ip pool cannot reach the internet. and they were not reachable from outside.
We advertised the /24 network to bgp neighbor . with change in static-route X.X.240.0 24 Null 0 , (for example we advertised X.X.240.0 /24)
with change in route we were able to advertise the routes in Bgp and ISP neighbor accepted the routes
we found that as per Internet Service Provider general policies , they do not accept the routes that are smaller than /24. (for example they will not accept route with subnet /26 or /28)
ISP routing policies should also be acquired for BGP advertisement.