Check your /etc/nginx/conf.d/local.conf file and see (around line 36) this location is aliased as follows:
location /.well-known/acme-challenge/ {
# This path must be served over HTTP for ACME domain validation.
# We map this to a special path where our TLS cert provisioning
# tool knows to store challenge response files.
alias /home/user-data/ssl/lets_encrypt/webroot/.well-known/acme-challenge/;
}
Then, the real location you asked for is:
/home/user-data/ssl/lets_encrypt/webroot/.well-known/acme-challenge/