Invalid json; The response is invalid json response

I have added contact form 7, embed it into ‘WP text’ along with the help of an ‘Pop Maker’ plugin.
As soon as I reload my window i got two errors saying
“Uncaught Error” :
“code: ‘invalid Json’, message: ‘The response is not a valid JSON response.’ “
And and then If I submit the form then as I submit the form get the same error again but this time without any “Uncaught error” heading and the form keeps on loading.
Need to resolve it in urgency.

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