@Emllyjoyce 

Try the following potential fix mentioned by @Howster:

Login into alexa.amazon.com on your laptop, click on Skills on the left nav, scroll down to the TP-Link Kasa icon, click it and click on the DISABLE SKILL button at the top. Once the skill is disabled go back and re-enable it by clicking on Enable on the top right. Enter the TP-Link Cloud log in credentials during the enablement process. Add your plug if required and try ON/OFF functionality again within the Alexa app. If you're in an "Amazon Household" account say to Alexa ""switch to John's account"" or whomever's account the plug is registered to. Last week I must have changed the password with some other TP-Link service (Tp-Link forum login, repeater setup, or whatever) but plugs or app dashboards never threw visuals error and were linked to the tp cloud with an invalid older password.