Error code for "Sendinblue plugin" for version 3.90 nopcommerce

Hello guys, i have succesfully installed the sendinblue plugin, but when i enter the API key i get this error message. Can you please help! Its the 24line that gives the error.

Server Error in '/' Application
Unexpected character encountered while parsing value: <. Path '', line 0, position 0.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: Newtonsoft.Json.JsonReaderException: Unexpected character encountered while parsing value: <. Path '', line 0, position 0.
Source Error:
Line 22: @if (!String.IsNullOrEmpty(Model.ConfigurationActionName))
Line 23: {
Line 24: @Html.Action(Model.ConfigurationActionName, Model.ConfigurationControllerName, Model.ConfigurationRouteValues);
Line 25: }
Line 26: else
Source File: h:\root\home\evertwice-001\www\smartmoto\Administration\Views\Plugin\ConfigureMiscPlugin.cshtml Line: 24