Error: UNSUPPORTED_API_VERSION: The API version that was specified (28.0) is below the minimum supported. Change the version number and run the request again.
The following error occurs when running the integration or when validating the Salesforce connection in SmartConnect 2018.
Cause
The underlying API version is no longer supported. This means your Salesforce org no longer supports such an outdated API version — v28.0 API End-of-Life. Salesforce periodically retires older API versions, and as of 2025, any version below v36.0 (and in many orgs, below v41.0) is no longer supported. In short, Salesforce is rejecting the connection because v28.0 falls below the minimum supported version.
How to Identify your Salesforce Edition and API Version: How to Identify your Salesforce Edition and API Version
For Example, if your Salesforce API version shows as 65.0 (Spring ’25 / Summer ’25) in the WSDL, you might assume that entering the same version in SmartConnect will work normally. However, that’s not the case — it will return an error:
“Login operation is not available in the API version specified (65.0).”
As of 2025:
• Salesforce supports API versions ~v40.0 through v65.0.
• SOAP login is available only up to about v57.0.
Reference: Ethan mentioned in point 2 that the default version 39.0 is set under the connection setup section. You can refer to this link for more details: Salesforce objects or fields are not available in SmartConnect.
Solution
- You’re currently using SmartConnect 2018, which relies on the SOAP login method. As seen in the connector setup, you can specify the API version there (typically ≤ v57.0).
However, it’s important to note that Salesforce may deprecate these versions soon — starting from API v50.0+, Salesforce began phasing out and eventually removing older SOAP login endpoints and methods from newer WSDLs.
Recommendation: If your integration still depends on SOAP login(), use API version ≤ 57.0 as a short-term solution, and plan to transition to OAuth 2.0 for long-term stability.
- To use the modern OAuth 2.0 method, you’ll need to upgrade from SmartConnect 2018 to SmartConnect 21 (the latest version). The OAuth 2.0 option is not available in SmartConnect 2018.
Setting up a Salesforce OAuth Connection
Therefore, it is recommended to proceed with Option 2 — upgrading SmartConnect.
If you decide to proceed with the upgrade, please review the following information:
https://www.eonesolutions.com/blog/moving-from-smartconnect-2018-to-smartconnect-21/
https://www.eonesolutions.com/video/moving-from-smartconnect-2018-to-smartconnect-21/
Notice: SOAP API login() call is being retired
The Salesforce Developer’s Guide to the Winter ’26 Release
As of Winter ’26 (API version 65.0), SOAP login() is no longer available. It will return an HTTP status code of 500 and the exception code UNSUPPORTED_API_VERSION.
You can continue to use login() the SOAP API versions 31.0 through 64.0 until Summer ’27 is released. At that time, login() these SOAP API versions will be retired and unavailable, and applications using this setup will experience disruption. The requests will fail with an error message indicating that the login() endpoint has been deactivated.
Before Summer ’27 is released, customers and partners must modify or upgrade their applications to use external client apps for authentication
Have a question? Please reach out to us at support@eonesolutions.com
