https://devzone.nordicsemi.com/f/nordic-q-a/85066/mqtt-using-ec-private-key-to-connect-to-a-brokerHi, I am using P822601 board (with nRF9160 chip). Sample project &quot;Serial lte modem&quot; (SDK 1.8). Faced a problem related to the inability to connect to the MQTT broker when using &quot;EC PRIVATE KEY&quot; via LTE Link Monitor. AT commands are used to connect: Howeveren-USTelligent Community 13Wed, 23 Feb 2022 10:07:09 GMThttps://devzone.nordicsemi.com/thread/354517?ContentTypeID=1Wed, 23 Feb 2022 10:07:09 GMT137ad170-7792-4731-bb38-c0d22fbe4515:b84d5656-4ff0-4dd6-a010-1b3a478f59bf&#216;yvind<p>Hello,&nbsp;<br /><br />Can it be due to an issue with certificate size?&nbsp;From the modem FW 1.3.1 release notes:</p> <blockquote> <ul> <li>- TLS/DTLS<br /> <ul> <li>Up to three simultaneous TLS/DTLS connections are possible.</li> <li>Maximum server certificate chain size has a limit of 4kB.</li> <li>Server certificate expiry time is not verified.</li> <li>pkcs#8 is not supported.</li> <li>Absolute maximum number of supported credentials is 32. The actual amount depends on size of credentials as memory area reserved for credentials may be a limiting factor as well.</li> <li>DTLS supports PSK authentication only.</li> <li>2kB secure socket buffer size.<br /><br /></li> </ul> </li> </ul> </blockquote> <p>Are you trying to connect to Amazon AWS? If so, please follow the <a href="https://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.9.0/nrf/libraries/networking/aws_iot.html#aws-iot">steps provided in our AWS IoT documentation</a>&nbsp;in regards to certificates.</p> <p>Kind regards,<br />Øyvind</p><div style="clear:both;"></div>