Welcome @venkatakrishna143
You have both an IPv4 A record and an IPv6 AAAA record in your DNS just for your api domain name
But, the IPv6 address points to a Hostinger service not your server. Hostinger creates this AAAA record automatically for new setups.
You need to update the AAAA address or remove it if you do not support IPv6.
Any client trying to use IPv6 will connect to that Hostinger service instead of your server.
Let's Encrypt favors IPv6 when an AAAA record is present.
See Hostinger article here: How to manage AAAA records | Hostinger Help Center
And use this site to test connections
https://letsdebug.net