Cannot connect to High Sierra using afp
https://support.apple.com/en-us/HT207828

AFP can’t share files on Apple File System (APFS). Apple File System (APFS) is the default file system in macOS High Sierra for Mac computers with all-flash storage. You can't opt out of the transition to APFS when you upgrade a Mac with all-flash storage to macOS High Sierra.
If you need to share files, switch to SMB. If you have network home directories shared via AFP on an APFS volume, update the mount records and user records to use SMB.