fastboot flashing error: "Partition should be flashed in fastbootd" I am new to android development and I am trying to flash a custom rom to my Pixel 3a. It was built through the android source project. But I am facing below error. If anyone has faced such an error, it will be great if you can help. Thank you.
user@user-Predator-PH315-52:~/aosp$ fastboot flashall -w
--------------------------------------------
Bootloader Version...: b4s4-0.2-5736883
Baseband Version.....: g670-00030-191028-B-5972069
Serial Number........: 9A9AY1CEC7
--------------------------------------------

Checking product

OKAY [  0.060s]

target reported max download size of 268435456 bytes

Erase successful, but not automatically formatting.

File system type raw not supported.

Erase successful, but not automatically formatting.

File system type raw not supported.

Sending 'boot_b' (65536 KB)...

OKAY [  2.340s]

Writing 'boot_b'...

OKAY [  0.346s]

Sending 'dtbo_b' (8192 KB)...

OKAY [  0.384s]

Writing 'dtbo_b'...

OKAY [  0.095s]

Sending sparse 'system_b' 1/5 (262140 KB)...

OKAY [  9.245s]

Writing 'system_b' 1/5...

FAILED (remote: Partition should be flashed in fastbootd)

Finished. Total time: 14.348s

**Phone**: Pixel 3a

**Build**: 9.0.0(PD2A.190115.032, Mar 2019)
I'm sure you figured it out by now but for any future users searching for a solution, I had the exact same issue on my Pixel 3a XL. You need the most up to date version of ADB and FASTBOOT. Grab it from Google to be sure you have the most recent, you only need the SDK Platform-Tools. Don't have to download the whole SDK Platform