Reverse lens using Nissin Di622 Mark II?

I use Nikon D5000. Just bought Nissin Di622 Mark II speedlight. Before, I used built in flash to shoot macro on reverse lens technique. I just need to set the built in flash to manual mode. Everything OK. But, when I used Di622, the camera detected that the the speedlight was in TTL mode even if I already set the Di622 to manual. When using reverse lens, if the speedlight in TTL mode, the camera unable to shoot.
Anyone has experience with reverse lens technique using Nissin Di622 Mark II, please help.

Added (1). My camera is already in manual mode.

Set your camera to manual mode.

Yes, your camera may be already in "Manual" and the Nissin is in "Manual"
but surely you still need to set the cameras flash setting to "Manual" ( instead of TTL)
then you can use the settings on the Nissin to control the flash output.

It's in the custom settings menu, "Optional Flash" e1 is the setting title, Page 162 of your manual.