Resolved thanks to this: https://webcache.googleusercontent.com/search?q=cache:ttFzMQPnzqUJ:https://discuss.redbear.cc/t/use-adafruit-bluefruit-app-to-substitute-redbear-ble-controller-app/4535+&cd=2&hl=en&ct=clnk&gl=uk
I needed to change the UUID on the SimpleChat RedBearDuo BLE example from:
static uint8_t service1_uuid[16] = { 0x71,0x3d,0x00,0x00,0x50,0x3e,0x4c,0x75,0xba,0x94,0x31,0x48,0xf1,0x8d,0x94,0x1e };
static uint8_t service1_tx_uuid[16] = { 0x71,0x3d,0x00,0x03,0x50,0x3e,0x4c,0x75,0xba,0x94,0x31,0x48,0xf1,0x8d,0x94,0x1e };
static uint8_t service1_rx_uuid[16] = { 0x71,0x3d,0x00,0x02,0x50,0x3e,0x4c,0x75,0xba,0x94,0x31,0x48,0xf1,0x8d,0x94,0x1e };
to the following:
static uint8_t service1_uuid[16] = { 0x6E, 0x40, 0x00, 0x01, 0xB5, 0xA3, 0xF3, 0x93, 0xE0, 0xA9, 0xE5, 0x0E, 0x24, 0xDC, 0xCA, 0x9E};
static uint8_t service1_tx_uuid[16] = { 0x6E, 0x40, 0x00, 0x02, 0xB5, 0xA3, 0xF3, 0x93, 0xE0, 0xA9, 0xE5, 0x0E, 0x24, 0xDC, 0xCA, 0x9E};
static uint8_t service1_rx_uuid[16] = { 0x6E, 0x40, 0x00, 0x03, 0xB5, 0xA3, 0xF3, 0x93, 0xE0, 0xA9, 0xE5, 0x0E, 0x24, 0xDC, 0xCA, 0x9E};