I2C slave does not work


We tested the example on this page:

On the terminal we keep getting
“Failed to write to slave!
Failed to read from slave!”

We made two new programs on the compiler; one for master and one for slave, and we broken down the example to master and slave. We are using I2C pins PB_7 and PB_6 for both master and slave boards. We have included resistors between the pins and 3.3V. Is the example wrong or are we doing something wrong?

Thank you,