no matching function for call to 'McuClass::begin()' for the Heltec Esp32 V2

[Saiyo14321]

I tried to test my heltec esp32 V2 on arduino IDE through using the examples form HeltecExample and I have tried all that codes from this HeltecExample I always get this "Compilation error: no matching function for call to 'McuClass::begin()'', sometimes its "error: 'SLOW_CLK_TPYE' was not declared in this scope" and error: 'HELTEC_BOARD' was not declared in this scope
btw, I am using the board manager URL: https://github.com/Heltec-Aaron-Lee/WiFi_Kit_series/releases/download/1.0.0/package_heltec_esp32_index.json
I hope you guys can help me fix this, I badly need the help bcoz we are stranded with this issue and cant start our coding for our thesis project.