You probably know that Idocs from purchase orders are sent via PO output messages.
So I wonder a bit what you see in SLG (whatever you mean by that)
Do you have an IDOC that just did not receive its destination, or don't you even have this IDoc and no message in your PO?
The 2 errors that you mentioned sound as if they are related to the EH&S module.
It looks like a classification is expected in your material master in case this material is REACH relevant. So I am not sure if these are real errors or just information that the requirement is not met and hence you wont get an IDoc.
Best you talk to your colleagues who had implemented this process in your company to get some insight about the preconditions and requirements.