Unable to add Topaz Denoise AI as an add on to Affinity Photo V2

[Jaffa]

My AP v2.4 runs on Windows.  I have checked on this forum and can't find anything specific which helps my question despite viewing posts on the topic.  I have added Topaz Denoise AI as an add-on, but when I do to edit a photo using the add on it is greyed out. 

Up to now I have edited the original file in Topaz Denoise AI then opened in AP V2, but would much rather use it as an add on - like I did with AP v1.

Here is a copy of my Settings

[RichardMH]

Are you applying DeNoise to a pixel layer? Try Merge Visible then applying DeNoise to that.

[Jaffa]

Many thanks, Richard, that's exactly what I had done this time!  A bit perplexed as to how it kept happening a few months back, when I tried with a number of images, when I certainly applied properly.   Never mind it works now and that's great!