Facebook text charges ?

[T5SWB]

Hi, hoping for a bit of advice please;

I have a pay monthly O2 contract with unlimited minutes and texts. I have just turned on my Facebook SMS notifications fo Marketplace and it informs me that although Facebook does not charge for this service my network provider (O2) ? 

I've tried to look it up on the internet but am confused when it refers to 'interactive' messages ?

Any clear guidance would be appreciated as I don't want to suddenly receive a huge bill at the end of the month.

Thanks in advance for any help

Regards, Gordon

[MI5]

@T5SWB 

No charge.

It's always free to receive text messages.

[T5SWB]

Thank you really appreciated your help

[MI5]

You're welcome