MailChimp Could Not Create SSL/TLS Secure Channel

Peeps' MailChimp Uploader

Peeps’ Software integrates with MailChimp, allowing stores to automatically add new consignors and customers to their MailChimp mailing list.

Recently, our app started returning the following error:

Could not create SSL/TLS secure channel

This is being caused by an older version of the TLS protocol, which MailChimp will no longer allow.

For anyone searching for this, I put this post out here to help any other developers trying to troubleshoot this.  There are a variety of results you’ll find when searching for this error, but it mainly comes down to the version of .NET your application targets.  The thing is though, that alone, isn’t the issue — e.g. your application needs to be targeting .NET version 4.5 or above in order to utilize the latest TLS protocol.

Your application could already be targeting .NET version 4.5, or even 4.7.2, and you’ll still get this error.

You have to explicitly specify the TLS protocol version before making your connection to MailChimp:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12

Once that’s set, you should be able to successfully connect to MailChimp again.  🙂

I am a Software Developer, System Administrator, and consignment software specialist. I currently manage hundreds of consignment workstations, point of sale systems, and database servers all across North America and I am the developer of Peeps' Software, Peeps2Go, and Peeps' Consignor Login for iOS and Android. I've been helping consignment & resale store-owners since 2003. I started The Computer Peeps in February of 2010. Peeps' Software launched in 2016 and is now on hundreds of systems all across North America. I have successfully converted dozens of stores from all of the major consignment software systems. After 20 years of working with consignment stores, I understand the unique challenges consignment & resale store-owners face. From electrical issues in old buildings or strip malls, to advocating for them when their old consignment software keeps crashing.

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