Working with I2C and port expander

[techykermit]

Hi!

I have not been working with I2C that much before, and I have a port expander (https://www.nxp.com/docs/en/data-sheet/PCAL6416A.pdf), which wants me to write data in bits. I am trying to write 8 bits to the "Configuration register pair", address hex 06 and hex 07, like this:

self.i2c.writeto_mem(self.write_address, 0x6, 0b00000000) #Write 0 to all 8 pins on the first port to turn them into outputs
self.i2c.writeto_mem(self.write_address, 0x7, 0b00000000) #Write 0 to all 8 pins on the second port to turn them into outputs

But I get an I2C bus error, which I assume is because I am not writing the bits correctly. Any ideas?