Issue interfacing FPGA SPI slave with ADBMS6822 isoSPI transceiver (works with STM32, not with FPGA)

I am using the EVAL-ADBMS6822 board. My system has the following components:

One ADBMS6822 configured as controller (MSTR=1).

One ADBMS6822 configured as peripheral (MSTR=0).

The peripheral transceiver's SPI pins are connected to an FPGA (Zybo Z7 board) in which I created a custom SPI slave in HDL.

VDD is at 3.3 V at slave side (this matches the FPGA I/O voltage).

Should be configured for Mode 3 (CPOL=1, CPHA=1) with PHAPOL.

XCVRMD is configured for standard 1 Mbps.

Common grounds are used, and isoSPI pair is connected IPIP, IMIM.

Observation:

Using an STM32 MCU as SPI slave, the ADBMS6822 evaluates LED blinks and communication works.

Using my FPGA slave, the LED is solid.

I verified that MISO goes tri-state when CS is high.

I am stuck and i don't know what to do, looking for any clues or insights