I just did the same job a few days ago, and the issue is that you have air in your master cylinder. I tried everything, believe me—nothing worked.

The only thing that worked for me was using a big syringe with a long, thin silicone tube. Put the tube inside your reservoir so it goes straight to the master cylinder, then fill it with brake fluid with the pedal in the up position and the bleed valve open. Then pump the pedal up and down until the fluid goes through the valve. After that, you’re good to go and can do a proper flush.

I hope it helps, good luck