Try =SUM((A1:A15o="rx")*(B1:B150="oem")), enterred as an array, type
the formula in and then CTRL/SHIFT/ENTER


There's a typo (A15o) in the formula.
Use this instead:
=SUM((A1:A150="rx")*(B1:B150="oem"))
Remember: Finish it by pressing Ctrl+Shift+Enter all together

As a reminder, we need to type Ctrl+Shift+Enter every time you change/edit the
formula or you double click the cell, or you may mistekenly change it back as a
simple function (NOT an array).
Also we can't set it as an array simply by enclosing the formula with { }, ie
{=SUM((A1:A15o="rx")*(B1:B150="oem")) }. We CANNOT do it in that way.