# SIM7600E-H Connection Error **URL:** \ **Category:** HiveMQ Cloud\ **Created:** [February 2, 2026, 12:38pm UTC](https://community.hivemq.com/t/sim7600e-h-connection-error/3990 "2026-02-02T12:38:59Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Gareth](https://avatars.discourse-cdn.com/v4/letter/g/ba8739/32.png) [@Gareth](https://community.hivemq.com/u/Gareth)\ **Post date:** [February 2, 2026, 12:38pm UTC](https://community.hivemq.com/t/sim7600e-h-connection-error/3990/1 "2026-02-02T12:38:59Z")
Hi I have been trying on and off for quite some time to connect the 7600E-H to HiveMQ without success. Tried just about everything I can think of as well as trawling the internet. I get error 6 "6 message receive fail” Here is the current connection attempt: OK AT+CNTP=“202.120.2.101”,32 OK AT+CNTP OK +CNTP: 0 AT+CCLK? +CCLK: “26/02/02,19:50:51+32” OK AT+CGDCONT=1,“IP”,“[mob.asm.net](http://mob.asm.net)” OK AT+CCERTLIST +CCERTLIST: “isrgrootx1.pem” OK AT+CSSLCFG=“cacert”,0,“isrgrootx1.pem” OK AT+CMQTTSTART +CMQTTSTART: 0 AT+CMQTTCONNECT=0,“tcp://140a405c2f3e4427aa4b1e83ea4d84d9.s1.eu.hivemq.cloud:8883”,60,1,“###”,“###” OK +CMQTTCONNECT: 0,6 +CMQTTCONNLOST: 0,1 A little help will be VERY much appreciated. ---
**Author:** ![Gareth](https://avatars.discourse-cdn.com/v4/letter/g/ba8739/32.png) [@Gareth](https://community.hivemq.com/u/Gareth)\ **Post date:** [February 2, 2026, 12:42pm UTC](https://community.hivemq.com/t/sim7600e-h-connection-error/3990/2 "2026-02-02T12:42:02Z")
Hi FYI: Here is uploading the cert: AT+CCERTDOWN=“isrgrootx1.pem”,1939 -----BEGIN CERTIFICATE----- MIIFazCCA1OgAwIBAgIRAIIQz7DSQONZRGPgu2OCiwAwDQYJKoZIhvcNAQELBQAw TzELMAkGA1UEBhMCVVMxKTAnBgNVBAoTIEludGVybmV0IFNlY3VyaXR5IFJlc2Vh cmNoIEdyb3VwMRUwEwYDVQQDEwxJU1JHIFJvb3QgWDEwHhcNMTUwNjA0MTEwNDM4 WhcNMzUwNjA0MTEwNDM4WjBPMQswCQYDVQQGEwJVUzEpMCcGA1UEChMgSW50ZXJu ZXQgU2VjdXJpdHkgUmVzZWFyY2ggR3JvdXAxFTATBgNVBAMTDElTUkcgUm9vdCBY MTCCAiIwDQYJKoZIhvcNAQEBBQADggIPADCCAgoCggIBAK3oJHP0FDfzm54rVygc h77ct984kIxuPOZXoHj3dcKi/vVqbvYATyjb3miGbESTtrFj/RQSa78f0uoxmyF+ 0TM8ukj13Xnfs7j/EvEhmkvBioZxaUpmZmyPfjxwv60pIgbz5MDmgK7iS4+3mX6U A5/TR5d8mUgjU+g4rk8Kb4Mu0UlXjIB0ttov0DiNewNwIRt18jA8+o+u3dpjq+sW T8KOEUt+zwvo/7V3LvSye0rgTBIlDHCNAymg4VMk7BPZ7hm/ELNKjD+Jo2FR3qyH B5T0Y3HsLuJvW5iB4YlcNHlsdu87kGJ55tukmi8mxdAQ4Q7e2RCOFvu396j3x+UC B5iPNgiV5+I3lg02dZ77DnKxHZu8A/lJBdiB3QW0KtZB6awBdpUKD9jf1b0SHzUv KBds0pjBqAlkd25HN7rOrFleaJ1/ctaJxQZBKT5ZPt0m9STJEadao0xAH0ahmbWn OlFuhjuefXKnEgV4We0+UXgVCwOPjdAvBbI+e0ocS3MFEvzG6uBQE3xDk3SzynTn jh8BCNAw1FtxNrQHusEwMFxIt4I7mKZ9YIqioymCzLq9gwQbooMDQaHWBfEbwrbw qHyGO0aoSCqI3Haadr8faqU9GY/rOPNk3sgrDQoo//fb4hVC1CLQJ13hef4Y53CI rU7m2Ys6xt0nUW7/vGT1M0NPAgMBAAGjQjBAMA4GA1UdDwEB/wQEAwIBBjAPBgNV HRMBAf8EBTADAQH/MB0GA1UdDgQWBBR5tFnme7bl5AFzgAiIyBpY9umbbjANBgkq hkiG9w0BAQsFAAOCAgEAVR9YqbyyqFDQDLHYGmkgJykIrGF1XIpu+ILlaS/V9lZL ubhzEFnTIZd+50xx+7LSYK05qAvqFyFWhfFQDlnrzuBZ6brJFe+GnY+EgPbk6ZGQ 3BebYhtF8GaV0nxvwuo77x/Py9auJ/GpsMiu/X1+mvoiBOv/2X/qkSsisRcOj/KK NFtY2PwByVS5uCbMiogziUwthDyC3+6WVwW6LLv3xLfHTjuCvjHIInNzktHCgKQ5 ORAzI4JMPJ+GslWYHb4phowim57iaztXOoJwTdwJx4nLCgdNbOhdjsnvzqvHu7Ur TkXWStAmzOVyyghqpZXjFaH3pO3JLF+l+/+sKAIuvtd7u+Nxe5AW0wdeRlN8NwdC jNPElpzVmbUq4JUagEiuTDkHzsxHpFKVK7q4+63SM1N95R1NbdWhscdCb+ZAJzVc oyi3B43njTOQ5yOf+1CceWxG1bQVs5ZufpsMljq4Ui0/1lvh+wjChP4kqKOJ2qxq 4RgqsahDYVvTH9w7jXbyLeiNdd8XM2w9U/t7y0Ff/9yi0GE44Za4rF2LN9d11TPA mRGunUHBcnWEvgJBQl9nJEiU0Zsnvgc/ubhPgXRR4Xq37Z0j4r7g1SgEEzwxA57d emyPxgcYxn/eR44/KJ4EBs+lVDR3veyJm+kXQ99b21/+jh5Xos1AnX5iItreGCc= -----END CERTIFICATE----- ---
**Author:** ![Daria\_H](https://avatars.discourse-cdn.com/v4/letter/d/dfb087/32.png) [@Daria\_H](https://community.hivemq.com/u/Daria_H)\ **Post date:** [February 16, 2026, 4:46pm UTC](https://community.hivemq.com/t/sim7600e-h-connection-error/3990/3 "2026-02-16T16:46:05Z")
Hi @Gareth thanks for sharing the detailed AT output, that’s very helpful. On SIM7600, the result code ```auto +CMQTTCONNECT: 0,6 ``` means **“message receive fail”** – the module didn’t get a valid MQTT CONNACK back. That usually points to a **TLS / transport issue** rather than wrong MQTT username/password. You’re already using the correct CA (`isrgrootx1.pem`, ISRG Root X1 from Let’s Encrypt), so the remaining pieces are the **TLS profile (including SNI)** and binding that profile to the MQTT client. Below is a configuration that is known to work with SIM7600 and HiveMQ Cloud. You can adapt it to your APN and your own cluster/credentials. * * * ### 1. Make sure the CA is installed correctly You already did this, but for completeness: ```auto AT+CCERTLIST ``` You should see: ```auto +CCERTLIST: isrgrootx1.pem ``` Optionally, you can verify the size: ```auto AT+FSCD="C:\" AT+FSCD="/mssl_cert/" AT+FSATTRI="isrgrootx1.pem" ``` The file size should be **1939 bytes** , which matches the standard ISRG Root X1 PEM from Let’s Encrypt (`https://letsencrypt.org/certs/isrgrootx1.pem`). * * * ### 2. Configure the TLS context (session 0) Run these once after network context is up: ```auto // Pick TLS 1.2 AT+CSSLCFG="sslversion",0,4 // Verify server certificate only (CA-based auth) AT+CSSLCFG="authmode",0,3 // Ignore local time (helps if RTC/NTP is slightly off) AT+CSSLCFG="ignorelocaltime",0,1 // Use the ISRG Root X1 CA you uploaded AT+CSSLCFG="cacert",0,"isrgrootx1.pem" // Allow all cipher suites (let server negotiate) AT+CSSLCFG="ciphersuites",0,0xFFFF // IMPORTANT: enable SNI for HiveMQ Cloud AT+CSSLCFG="enableSNI",0,1 // Check the full TLS config AT+CSSLCFG? ``` SNI is required for HiveMQ Cloud, and without `enableSNI` the TLS handshake often fails without a clear error, which then shows up as `+CMQTTCONNECT: 0,6`. * * * ### 3. Start MQTT and bind SSL to the MQTT client After PDP context and `AT+NETOPEN` succeed: ```auto // Start MQTT stack AT+CMQTTSTART // Create MQTT client 0 with a client ID (QoS 1, clean session) AT+CMQTTACCQ=0,"sim7600_client",1,4 // Bind MQTT client 0 to TLS session 0 configured above AT+CMQTTSSLCFG=0,0 // Now connect to HiveMQ Cloud over TLS AT+CMQTTCONNECT=0,"tcp://140a405c2f3e4427aa4b1e83ea4d84d9.s1.eu.hivemq.cloud:8883",60,1,"YOUR_USERNAME","YOUR_PASSWORD" ``` Replace `YOUR_USERNAME` and `YOUR_PASSWORD` with the access credentials you created in the HiveMQ Cloud UI. If everything is correct, you should see: ```auto OK +CMQTTCONNECT: 0,0 ``` instead of `0,6`. * * * ### 4. Sanity check the credentials (optional but recommended) From a PC, you can verify hostname/port/credentials independently using an MQTT client, for example `mqtt-cli`: ```auto mqtt sub -h 140a405c2f3e4427aa4b1e83ea4d84d9.s1.eu.hivemq.cloud -p 8883 -s -u YOUR_USERNAME -pw -t 'test/topic' ``` If that works, your hostname, port, and credentials are definitely fine, and any remaining problem is purely on the SIM7600 side (TLS/SNI or APN/network). Best regards, Dasha from the HiveMQ Team ---
**Author:** ![Gareth](https://avatars.discourse-cdn.com/v4/letter/g/ba8739/32.png) [@Gareth](https://community.hivemq.com/u/Gareth)\ **Post date:** [February 21, 2026, 10:18am UTC](https://community.hivemq.com/t/sim7600e-h-connection-error/3990/4 "2026-02-21T10:18:17Z")
Hi Thank you so much for this, but it still does not work. I get error 33 (not set certificate) AT+CMQTTCONNECT=0,“tcp://140a405c2f3e4427aa4b1e83ea4d84d9.s1.eu.hivemq.cloud:8883”,60,1,“xxxx”,“xxxx” OK +CMQTTCONNECT: 0,33 AT+CSSLCFG? +CSSLCFG: 0,4,3,1,300,“isrgrootx1.pem”,“”,“”,1,“”,0xFFFF +CSSLCFG: 1,4,0,1,300,“”,“”,“”,0,“”,0xFFFF +CSSLCFG: 2,4,0,1,300,“”,“”,“”,0,“”,0xFFFF +CSSLCFG: 3,4,0,1,300,“”,“”,“”,0,“”,0xFFFF +CSSLCFG: 4,4,0,1,300,“”,“”,“”,0,“”,0xFFFF +CSSLCFG: 5,4,0,1,300,“”,“”,“”,0,“”,0xFFFF +CSSLCFG: 6,4,0,1,300,“”,“”,“”,0,“”,0xFFFF +CSSLCFG: 7,4,0,1,300,“”,“”,“”,0,“”,0xFFFF +CSSLCFG: 8,4,0,1,300,“”,“”,“”,0,“”,0xFFFF +CSSLCFG: 9,4,0,1,300,“”,“”,“”,0,“”,0xFFFF I’ve tried: AT+CMQTTSSLCFG=0,0 OK AT+CMQTTCONNECT=0,“tcp://140a405c2f3e4427aa4b1e83ea4d84d9.s1.eu.hivemq.cloud:8883”,60,1,“xxxx”,“xxxx” OK +CMQTTCONNECT: 0,33 AT+CMQTTSSLCFG=0,1 OK AT+CMQTTCONNECT=0,“tcp://140a405c2f3e4427aa4b1e83ea4d84d9.s1.eu.hivemq.cloud:8883”,60,1,“xxxx”,“xxxx” OK +CMQTTCONNECT: 0,31 AT+CMQTTCONNECT=0,“tcp://140a405c2f3e4427aa4b1e83ea4d84d9.s1.eu.hivemq.cloud:8883”,60,1,“xxxxx”,“xxxxxx” OK I’m giving up hope here…. It works with Mosquito, but this dev project is for a large(ish) scale deployment and I do not want to host a server etc, I REALLY want to use HiveMQ but don’t know what to do next. Any further help would really be appreciated. ---
**Author:** ![SShet](https://avatars.discourse-cdn.com/v4/letter/s/b3f665/32.png) [@SShet](https://community.hivemq.com/u/SShet)\ **Post date:** [February 25, 2026, 9:34am UTC](https://community.hivemq.com/t/sim7600e-h-connection-error/3990/5 "2026-02-25T09:34:52Z")
Hello @Gareth thank you for sharing the detailed AT command logs. From the output, we can see that your modem’s SSL context 0 is configured with: - A CA certificate: `isrgrootx1.pem` Download it form [here](https://letsencrypt.org/certs/isrgrootx1.pem) - `authmode = 3` (verify server **and** client certificate) - No client certificate and no client key configured In this configuration, the module expects a client certificate/key pair for mutual TLS. Since no client certificate is set, the modem reports `+CMQTTCONNECT: 0,33` (“not set certificate”). HiveMQ Cloud only requires: - TLS with the correct CA (Let’s Encrypt ISRG Root X1) - Username and password authentication A client certificate is **not** needed, so we recommend switching to server‑only authentication on the modem. Please try the following sequence (after ensuring `isrgrootx1.pem` is already on the module): 1. Configure TLS context 0 (run once, or after a reset) ```auto AT+CMEE=2 AT+CSSLCFG="sslversion",0,3 AT+CSSLCFG="authmode",0,1 AT+CSSLCFG="cacert",0,"isrgrootx1.pem" -- Optional but recommended, if supported by your firmware: AT+CSSLCFG="sni",0,"140a405c2f3e4427aa4b1e83ea4d84d9.s1.eu.hivemq.cloud" -- or AT+CSSLCFG="enableSNI",0,1 ``` You can verify the SSL context with: ```auto AT+CSSLCFG? ``` Context **0** should now show `authmode` = 1 and `cacert = "isrgrootx1.pem"`. 1. MQTT connection sequence to HiveMQ Cloud ```auto AT+CMQTTSTART AT+CMQTTACCQ=0,"client-id",1 AT+CMQTTSSLCFG=0,0 AT+CMQTTCONNECT=0,"tcp://140a405c2f3e4427aa4b1e83ea4d84d9.s1.eu.hivemq.cloud:8883",60,1,"username","password" ``` Where: - `client-id` is any unique MQTT client ID. - `cloud-username` and `cloud-password` are the credentials from **Access Management** in your HiveMQ Cloud cluster. If you still see a different CMQTTCONNECT error code after this change, please send us the updated AT log (including `AT+CSSLCFG?` and `AT+CCLK?`) Best regards, Sheetal from HiveMQ Team ---
**Author:** ![Gareth](https://avatars.discourse-cdn.com/v4/letter/g/ba8739/32.png) [@Gareth](https://community.hivemq.com/u/Gareth)\ **Post date:** [March 25, 2026, 6:35am UTC](https://community.hivemq.com/t/sim7600e-h-connection-error/3990/6 "2026-03-25T06:35:59Z")
Hi I am so sorry my reply has been so delayed - I have been pulled this way and that on projects - you know how it is… Anyway, this worked! Phew! Thank you so much for taking the time to help me through this in what in the end was a stupid error on my part.