Failed to initialize audio spatializer?

I don't get it. Unity 6, Meta sdk 72.

My audio spatializer settings are both with Meta XR audio settings and everything as shown in some officialdocumentation I found online. But I get this message:

Audio source failed to initialize audio spatializer. Please check that the project audio settings and make sure that the selected spatializer is compatible with the target.

Also sometimes actually it does spatialize the audio, even with this message. But sometimes I cannot get it...

Please, is there any straight forward solution for this basic thing?

Thanks in advance