I have downloaded and tried out pooler cpuminer (from
https://sourceforge.net/projects/cpuminer/) to see how mining on CPU would turn out, and it seems I'm still getting the same "stratum requested work restart" message...
That message means the pool is working. You haven't been able to mine sha256d with a CPU or GPU for 10 years.
Only high powered ASICS are suitable for sha256d.
You need to do more research.
You're right. I'm still very new to this. Thanks for all your help!