Hello @keerthisri123,
In order to support you better, could you provide me the next information?
-Are you using the same external flash device as the RT1010-EVK? If not, could you please provide the part number of the flash device used on your custom board?
-Which image are you attempting to program? Is it an SDK example or your own custom application?
-Which tool are you using to program the device? For example MCUxpresso IDE, Secure provisioning tool, etc?
-Are you connected through JTAG or SWD?
If there are any additional details you believe could help, please do not hesitate to let me know.
BR
Habib