Error presenting challenge: ingress.networking.k8s.io "nginx" not found

I was following tutorial present at - https://www.digitalocean.com/community/tutorials/how-to-set-up-an-nginx-ingress-on-digitalocean-kubernetes-using-helm . When I try securing my ingress using Cert-Manager, I am able to create certificate but it is not working. Upon “kubectl describe certificate -o wide” I see Ready=False for the certificate and the reason/status it shows is **Issuing certificate as Secret does not contain a private key. ** Looking deeper and troubleshooting, I found that “kubectl describe challenges -o wide” gives STATE=pending and REASON=Error presenting challenge: ingress.networking.k8s.io “nginx” not found. Please suggest the cause as well as solution for this issue as I am unable to get any insight from anywhere for this. Thanks!