Firstly – THANK YOU ALL for your help!
a. this indeed creates the file.
echo “Test” > c:\wwwroot.well-known\acme-challenge\123.txt
b. I now believe the “not writable folder” also comes if you have an error in the folder path string. Using c:\wwwroot888.well-known\acme-challenge\123.txt gives the same error.
I now think I had the folder right to start – and getting NO error was the correct thing.
c. Current state
When I run the Windows 64 bit binary, with the below string
le64 --key account.key --csr fundamentalobjects.csr --csr-key mydomain.key --crt mydomain.crt --domains www.fundamentalobjects.com,fundamentalobjects.com --path c:\wwwroot\.well-known\acme-challenge\ --generate-missing --update-contacts myemail@fundamentalobjects.com
I get only this output
2018/08/26 10:01:23 [ ZeroSSL Crypt::LE client v0.31 started. ]
2018/08/26 10:01:23 Loading an account key from account.key
2018/08/26 10:01:25 Registering the account key
2018/08/26 10:01:26 The key is already registered. ID: my number here
2018/08/26 10:01:26 Current contact details: myemail@fundamentalobjects.com
2018/08/26 10:01:26 Contact details have been updated.
No files created in acme-challenge or other files modified.