I had a problem and got it solved
Quote
If you go to the arduino IDE board manager (ctr + shift + B) and look for “esp8266 by ESP8266 Community” you should select to install version 2.7.4
any version above 3.0.0 does not have the required functions at this moment
unQuote
How to do in PIO ?
As per documentation you can select the to be used platform version for Espressif8266 that is then linked to he used Arduino core version per Releases · platformio/platform-espressif8266 · GitHub.
The last platform version to use core 2.7.4 is
platform = espressif8266@ 2.6.3
Thanks for info now I understand how I shuld have done !
I followed your instructions but found that I should use 2.6.2 as I understod 2.6.3 has 3.0
I will test tomorrow it’s late already here in Thailand. 
Thanks again for very quick support.
Bjorn
No it only upgraded esptool.py to version 3.0, that is not the Arduino core.
So platform-espressif8266 @ 2.6.3 uses Arduino-ESP8266 2.7.4.
Pls bare with me now I understand maybe I can hide behind I was sales until I retiered.
Thanks 