ISR for SPI on Wio Terminal

The line:

ISR (SPI_STC_vect)

generates the “expected constructor, destructor…” error on the Wio Terminal, and all other Seeed boards I tried. It works fine on lots of Arduino boards. I’ve also experimented with ISR for internal timers, and same thing - good on an Arduino Uno, but the same error on Seeeds.

Is this a <SPI.h> library issue, or is ISR not the right command for Seeed board internal interrupts?
Thanks!

Forgot to mention: I’m trying to make an SPI slave out of the Wio Terminal.