Base: Run macro on form open

I’m sure that I’m missing something simple here but how do I get a macro to run on initial opening of a form?

I have created a macro & assigned it to the ‘When Loading’ event of the form ut nothing happens. I have even set the macro to just display a ‘MsgBox’ message (rather than do anything clever) but it is still not being executed. Assigning the same macro to a command button on the same form works OK when it is clicked, just not on form opening. Am I missing the point here somewhere or using the wrong event?

https://forum.openoffice.org/en/forum/viewtopic.php?f=39&t=34147&p=184762&hilit=open+form+on+load#p184762