The data sheet you sent to me mention “Vortex” type meter, please clarify.
Furthermore the fluid is “oily water” which most almost certainly is not enough conductive: as you know the minimum conductivity level for electromagnetic flowmeters is 5µS;
this explains also the result of test between A-B is 0.
Please check with your customer the conductivity and revert to me accordingly.
I’m persuaded that the meter works correctly; it is imperative to follow step by step the directives for correct installation and start-up.