tls: failed to verify certificate: x509: certificate signed by unknown authority

Hello,
my app is trying to send a post request to an existing API (ntfy.sh) but I got this error message:
“tls: failed to verify certificate: x509: certificate signed by unknown authority”

What should I do to handle this? Can anybody help me?
Thank you in advance!

I found the solution.
My docker image was built from a simple ubuntu that misses the ca-certificates package.
After I add this to my Dockerfile (‘RUN apt update && apt install -y ca-certificates’) it works