OTA through at+ciupdate

[shar_tkt]

Hi ,
With default AT firmware and following instructions mentioned in AT manual(Ch 8 - OTA update) , I was expecting custom firmware flashed over air , but there seems to be some issue.
- Used the bin generated from "http://iot.espressif.com" and with ota token as mentioned in manual in menuconfig.
- Flashed manually (Ota capable) as to reflash similar over the air for test.
- Getting "rom_version error!" and seems debugging wont help much.

Manual is not clear whether needs custom firmware:
If using Espressif’s AT BIN (/esp-idf/bin/at), AT+CIUPDATE will download a new AT BIN from the
Espressif Cloud
- Does this mean (bin location not present) special AT bin which is not available?

If using a user-compiled AT BIN, users need to make their own AT+CIUPDATE upgrade. Espressif
provides a demo as a reference for local upgrade (/esp-idf/example/at).
- Does this mean user compiled bin (which I have done) needs custom implementation as binary layout might have changed,
again example location is not available.

Also is there any guide if third party cloud need to be used?
"ESP8266 FOTA Guide" -Is this relevant to ESP32 also?

rgds,
shar_tkt