Help with setting custom white balance

[Grumpy John]

I am trying to set the custom white balance on my Canon R6 for use with a R72 infra red filter. When I take and image of green grass (as recommended) the image is red, when I try to set this image as a reference I get the message "Correct WB may not be obtained with the selected image". Am I doing something wrong, or is the white balance of the R6 not able to be set for IR photography?

[ameerat42]

What colour were you expecting the grass to be?

In days of yore, when Kodak IR Ektachrome was de rigueur, highly
IR-reflective subjects, like vegetation, were rendered red. Blue skies often had a
touch of green, and (white) peoples faces looked pasty, so you may already
have it right enough.

[ameerat42]

PS: Through a Wratten Yellow (15 I think) filter.