https://devzone.nordicsemi.com/f/nordic-q-a/809/why-return-different-results-between-and-when-i-run-the-same-programHi, After i use sd_ble_gatts_hvx() ,i will receive a BLE_EVT_TX_COMPLETE. The &quot;tx_complete.count&quot; is no problem when i use softdevice 5.2.1 . e.g. count =1. this is correct. But the &quot;tx_complete.count&quot; is wrong when i use softdevice 6.0.0-1 . een-USTelligent Community 13Fri, 01 Nov 2013 09:12:32 GMThttps://devzone.nordicsemi.com/thread/4025?ContentTypeID=1Fri, 01 Nov 2013 09:12:32 GMT137ad170-7792-4731-bb38-c0d22fbe4515:8afb7360-055c-4722-b8b6-8bd32ed82dd1Ole Morten<p>I just tested it, and as far as I can see this will happen if you use the 5.2.1 header files with the 6.0.0 softdevice.</p> <p>You should always take care to compile your application with the header files that came with the softdevice you&#39;re using, but this is of even higher importance when there are functionality and API changes (i.e. when there is a major version increment). When not doing this, you may see strange return errors (in case of changing SVC numbers) or wrong event data (in case of event structs changing). When using the correct header files, your compiler will take care of this.</p><div style="clear:both;"></div>