How to pair/connect with a MAC address

I need to connect to other units according to heir MAC address. I'm assuming that this:

BT_SCAN_FILTER_TYPE_ADDR
Is the thing to use in this:
bt_scan_filter_add
So instead of this:
err = bt_scan_filter_add(BT_SCAN_FILTER_TYPE_UUID, BT_UUID_XLRT_SERVICE);
You'd have this:
err = bt_scan_filter_add(BT_SCAN_FILTER_TYPE_ADDR, BT_MAC_ADDRESS);
I can see that you do this:

#define BT_UUID_XLRT_SERVICE BT_UUID_DECLARE_128(XLRT_SERVICE_UUID_VAL)

Where this:

#define XLRT_SERVICE_UUID_VAL \
BT_UUID_128_ENCODE(0x2a1f963c, 0x143a, 0x4f7d, 0x9107, 0x6315196a02a6)
Has been previously defined, but what's the syntax for defining something like BT_MAC_ADDRESS
please? Would be so helpful if you had little code snippets of how to do stuff like this.
Thanks
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