So it is not possible when clicking the button to create the mail? I have to do an APP?
As mentioned, the below implementation will help you to Identify the difference in the Power Apps Itself and the changes can be mentioned in the E-Mail. I am bit confused with your query.
Regarding the flow error Your Select action Map is invalid JSON, which is why Power Automate shows: “Enter a valid json” Also, your Send HTTP request is failing because it depends on the broken Select output. Can you please share the full flow screenshot
In Select action, configure like this: split(variables('YourString'), ';')
Title : replace(replace(split(item(), ':')[0], '"',''),'''','')
Previous value : replace(replace(split(item(), ':')[1], '"',''),'''','')
Current value : body('Send_an_HTTP_request_to_SharePoint_2')?['body']?[json(item())]
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