Thanks. curl/acme.sh can't communicate with Let's Encrypt, because your operating system and its packages are too out-of-date.
The preferred option is going to be to upgrade to a maintained version of SLES.
You could also try the workaround I posted here, keeping in mind that those instructions are for Ubuntu and may need to be adjusted for SLES. It's possible also that the instructions won't work, if the problem is the age of your OpenSSL package.