mqtt_simple example: mqtt_connect error -12

Question

Hello everyone, 
 I started an evaluation for the Nordic Thingy91 using the "mqtt_simple" example from the SDK1.6.0 version. The Thingy91 is HW-version 1.4.0. Programming is done in SES V5.50c. 
 The standard-example works (which connects to mqtt.eclipseprojects.io). 
 I tried to connect to another server without a username and a password and it also worked as intended. I did this by changing the "MQTT_BROKER_HOSTNAME" in Kconfig and the "CONFIG_MQTT_BROKER_HOSTNAME" in prj.conf. I know, only the prj.conf needs to be changed, I changed both to be sure. 
 
 Then I changed the host a server which need a specific username or a password. TLS is not used. 
 I added the username and password in the main.c: 
 
 The result is "mqtt_connect -12": 
 
 I found this topic ( mqtt connect error - Nordic Q&A - Nordic DevZone - Nordic DevZone (nordicsemi.com) ) and increased the buffer size in the prj.conf and Kconfig to 512: 
 CONFIG_MQTT_MESSAGE_BUFFER_SIZE=512 CONFIG_MQTT_PAYLOAD_BUFFER_SIZE=512 
 In the mentioned topic, the connect error -12 was solved by increasing buffer sizes. For me, the problem persisted, as shown in the second picture. 
 
 What can I do to find the error? 
 With other MQTT Clients I can connect to the server using the same username and password,

Øyvind · Accepted Answer

Hey Chris,

Sorry, I forgot to clarify that both password and user_name are structs with a pointer and a size Ref. zephyr\include\net\mqtt.h

/** @brief Abstracts UTF-8 encoded strings. */
struct mqtt_utf8 {
	const uint8_t *utf8;       /**< Pointer to UTF-8 string. */
	uint32_t size;             /**< Size of UTF string, in bytes. */
};

Please retry with the following, tested by our developer and should work with your application:

struct mqtt_utf8 password = {
 .utf8 = "password",
 .size = strlen("password")
 };
 
 struct mqtt_utf8 username = {
 .utf8 = "username",
 .size = strlen("username")
 };
 
 /* MQTT client configuration */
 client->broker = &broker;
 client->evt_cb = mqtt_evt_handler;
 client->client_id.utf8 = client_id_get();
 client->client_id.size = strlen(client->client_id.utf8);
 client->password = &password;
 client->user_name = &username;
 client->protocol_version = MQTT_VERSION_3_1_1;

Kind regards,
Øyvind

mqtt_simple example: mqtt_connect error -12

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