nRF52 SDK14.2 ble_app_uart (peripheral) example not working

Question

I downloaded SDK14.2 and loaded S132 v5.0 and then compiled and loaded the ble_app_uart example code (I also tried the precompiled hex provided with the SDK). It all compiles and loads just fine, but when I try to communicate with the bluetooth module using the nRF Toolbox app (on iOS), it doesn't work. In the nRF Toolbox app, the log says: 
 "Enabling notifications failed" 
 "Error Writing is not permitted." 
 I looked at the logs and I see that the BLE_GATTC_EVT_EXCHANGE_MTU_RSP event occurs for some reason. This seems very similar to this question, so I tried all the recommendations from that thread without success. I messed with the optimization and updated everything to S132 v5.1, which did not work. 
 Any ideas?

Mostafa Berg · Accepted Answer

Hi @timmey9 ! 
 There could be a few reasons causing this so it's hard to tell the exact cause, I've personally experienced the writing not permitted bug on iOS while flashing multiple examples on the same dev kit and connecting the same phone, my reason was that some example had the GATT table in a different order, causing this issue, I would try to tackle this issue first, what you can do to confirm is 
 
 Try it on a different iPhone 
 Try it on a different platform 
 
 if it works correctly on a different iPhone or a different platform like Desktop/Android, then your issue is probably due to the "corrupted" GATT table, easiest way I managed to fix this is to turn off bluetooth from the settings menu and NOT from the control center, for 10 seconds, then turn it on again. also if the BLE peripheral is in your connected peripherals list in the bluetooth settings menu, make sure to select it then tap "forget device" before toggling bluetooth to ensure it has been completely removed from iOS. 
 if that isn't the issue let us know and we can look further

nRF52 SDK14.2 ble_app_uart (peripheral) example not working

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