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ESP32 fails to connect to MQTT... Error Code = -4

We have been working on sending some data on UBIDOTS using MQTT. We have been experiencing some issues related to connection to MQTT server with the following error:

Attempting MQTT connection…failed, rc=-4 try again in 3 seconds

Everything was working fine earlier. Suddenly, today it has started giving this error.

We have tried to connect ESP32 to different networks, but all in vain.

Please help.

Hello @divneet, according to the return code, it seems to be an error related to the credentials, as the connection is not going through

MQTT return code -4: Connection timeout.

Please remember that Ubidots’ MQTT broker endpoint is industrial.api.ubidots.com

Take a look at this article, as it might help you on getting a proper connection via MQTT on your ESP32 with Ubidots.

@divneet, after some testing and investigation, it looks like it’s a version issue with the library. Could you please try again but this time using this library?

I’ll be attentive to your response.

Thanks for the reply.
We made MQTT broker endpoint changes to industrial.api.ubidots.com, and it worked.
Surprisingly, it is also working now for things.ubidots.com as well.
I believe there was MQTT server error for that day only.

I will also update the library, and get back to you soon.

Thanks for the support.