This thread is about the SKR mini e3 v1.2 which has a STM32F103C8 instead of your LPC1768. So I hope you didn’t use any of the platformio.ini files here to create your project.
There is also a similiar thread in How do I set my start offset(Bootloader) which matches your LPC1768, uses the official nxplpc platform and the mbed framework.
I also have a base project here:
Can you open a new thread about your specific problem, what platformio.ini you’re using, what flash offset you’ve set for the bootloader, et cetera?