Can someone please help

Mabey try, In the menu setting, speakers, speaker config., front small or large. Guessing it will be small, but do both to see. Have subwoofer to yes. Also check amp assign. 

It’s gotta be something in the audio setup settings. Rather than racking your brain and wasting more time I agree just contact Denon as they can probably answer your question in about 10 seconds.

 If “Speaker Config.” - “Front” and “Center” are set to “Large”, and “Subwoofer Mode” is set to “LFE”, no sound may be output from the subwoofers, depending on the input signal or selected sound mode. (v p. 184)
Select “LFE+Main” if you want the bass signals to always be produced from the subwoofer.

Owner's Manual Page 191

I just hooked up the denon avr-s760h. Currently just trying to play music thru Bluetooth.

I’m only running a front left, front right, and a sub. Fr fl hooked up to fr and fl outputs on receiver. Sub hooked up to sub 1 output https://vidmate.onl/ .

I can not get the sub to play. If I put it on surround mode only the sub plays. So I know it works. When I put it back on stereo mode there is only a “FR” and “fl” level adjustment. So sub adjustment so it’s like the receiver doesn’t think a sun is hooked up.

i got this .....

RTFM