Single Value Invalid field!

Im having this problem where I have a Macro: FILLNULL | eval POINT = case(Forecast>=SLA ,Forecast) | fields POINT | delta POINT | where POINT>0 | fields _time | head 1 | convert ctime(_time) as MY

I want to use this macro to populate a "Single Value" on my dashboard:

 <module name="ViewstateAdapter">
                                <param name="strictMode">True</param>
                                <module name="HiddenPostProcess">
                                        <param name="search">`SLA_TouchPAD`</param>
                                                <module name="SingleValue">
                                                        <param name="field">MY</param>
                                                 <param name="beforeLabel">TouchPad:</param>
                                                </module>
                                        </module>
                                </module>
                        </module>

But for some reason no matter what I do it displays that the field is Invalid?

I noticed others were having problems with this, but the search that my postprocesses adds to, only uses the exact fields that are extracted from the end of the main search, so what's the problem here?

I have taken a look at the UI_Examples app, not much help there in this case.