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.

[Dev]

I do get further packets changing the connection data length (to 27) and the MTU to 23 so perhaps it is busy because it wants to change these parameters?

In which case I would have to perform the discovery later somehow; there doesn't seem to be any code to try again for the characteristics at least.

I could just start the entire process over but it seems that the same issue would occur.