When you are the first time to debug LPC55S69, please read below document and double check your IDE, SDK and EVK version is correct.
Usually, we prefer use the latest IDE, SDK and EVK boards.
Important updates when using LPCXpresso55S69 Revision A2 boards and 1B silicon
When you use IAR 8.32 to debug LPC55S69 '1B' silicon, the IDE will remind you "The debugging session could not be started", like below picture show:
The reason of this failure is that IAR 8.32's LPC55S69 chip configuration files only support revision '0A' silicon, not '1B'.
We strongly recommend customer download and use IAR 8.40.2 or latest version. The IAR IDE start support LPC55S68 '1B' silicon from 8.40.2.
If you have some reasons that must use IAR 8.32, you can download attached zip file. This zip file like a patch, include the IAR LPC55S69 '1B' support files.
Un-zip this file and merge the same files under IAR installed path :IAR\arm\config\flashloader\NXP
Then the IAR can support '1B' silicons.
[How to identify LPC55(S)6x chip silicon versions]
On the top-side marking code, there is '1B' charactors at the end of mark strings. See below two pictures, the left one is '1B' version chips.
LPC55(S)6x ver '1B' LPC55(S)6x ver '0A'