Before you configure URL rewriting or redirects, make sure Web Dispatcher can connect to your SAP system by running sapwebdisp pf=<profile> -checkconfig. It appears that your config is wrong:
ms/http_port = 8100 (Web Dispatcher)
ms/server_port_0 = PROT=HTTP,PORT=81$$ (SAP system)
unless your SAP system number is actually 00. I assume it is 71, change to
ms/http_port = 8171 (Web Dispatcher)
and retry.