Check this page in your Vultr account and be sure the BGP is listed there. https://my.vultr.com/network/#network-bgp
A couple of tips on bird.conf. Use the following router statement instead of the one with the static IP address to pick up whatever IP is assigned by Vultr to ens3 between VPS rebuilds.
router id from "ens3";
The "source address..." statement in the "protocol bgp" section is not required. It will default to the IP connected to "neighbor".
I did not require a "protocol static" section.
These bird.conf changes seem to let me recreate the bgp VPS with a new Vultr IP address and bgp will continue to function.
David M. WD5M