ERROR:Connection Request Failed, reason 7

[Dev]

I am using a NRF52-based platform and have BLE code based on the ble_app_hrs_c Hear rate monitor system.

Having set up for scan, I see many device (we have a lot of beacons around).

I can also see the device I wish to connect to and even read values advertised, such as RSSI.

However, when I attempt connection, the call returns with the above error.

I looked a the SDK code (13.0.0) and that error seems to be invalid parameter.

I have checked through the parameters and they are as in the example. I did modify most of the parameters one by one to no avail.

I also checked the stack init, it is identical to the example.

I have no whitelisting.

Since the scan works, BLE is obviously operating.

Is there a noob issue I am missing, although I am not a noob to BLE or BT in general.

[Dev]

It would appear that, somewhere, someone missed something.

I decided to restart from the example and match up, line by line.

It seems that the previous engineer decided not to register service UUIDs, which seems reasonable since we are only interested in reading services, not advertising them.

However, after registering one, arbitrarily choosing the Heart Rate service, the discovery worked.

Now, all I have to do is proceed through the rest of the requirements to actually read a characteristic.

[Petter Myhre]

If it helped changing the MAX MTU you service discovery probably conflicts with the ATT MTU Exchange procedure (sd_ble_gattc_exchange_mtu_request() + BLE_GATTC_EVT_EXCHANGE_MTU_RSP), see this for more information. What if you initiate the service discovery when you get the NRF_BLE_GATT_EVT_ATT_MTU_UPDATED event in gatt_evt_handler()?