Can't import own ringtone through itunes 12.9.4

I've done this a couple of times before in earlier Itunes releases. Even with Itunes 12.7, so I do know about the changes that was made in Itunes according to ringtones then. The ringtone I try to import this time is approximal 10 seconds long. I have other ringtones that is 14 and 15 seconds long. When I do the "drag and drop" move (taking the m4r file from windows file explorer and dragging it over to Itunes over the sidebar part for "My device" where the blue frame and field reveals) in Itunes to my device I get a message that says something like (translated from Swedish so I don't know the exact formulation in English): "Ringtone "Signal.m4r" did not copy to iPhone unit "iPhoneName" because it's time length is too long."

I've tried to shorten the tone to between 5 and 6 seconds with the same result. I've event tried to compress the file size really really hard. Also with the same result.

My m4r-file has a unique name in my Itunes library.

Anybody encountered this, have a solution or can tell me what I'm doing wrong?