WARNINGS: PostmanUtils.php on line 68

I get these warnings when I update a Visual composer page. The pluin seems to work ok.
Warning: substr() expects parameter 1 to be string, array given in /home/samyrugema/public_html/wp-content/plugins/postman-smtp/Postman/PostmanUtils.php on line 68

Warning: substr() expects parameter 1 to be string, array given in /home/samyrugema/public_html/wp-content/plugins/postman-smtp/Postman/PostmanUtils.php on line 68

Warning: session_start(): Cannot send session cache limiter – headers already sent (output started at /home/samyrugema/public_html/wp-content/plugins/postman-smtp/Postman/PostmanUtils.php:68) in /home/samyrugema/public_html/wp-content/themes/lifeline/functions.php on line 18

Warning: substr() expects parameter 1 to be string, array given in /home/samyrugema/public_html/wp-content/plugins/postman-smtp/Postman/PostmanUtils.php on line 68

Warning: substr() expects parameter 1 to be string, array given in …plugins/postman-smtp/Postman/PostmanUtils.php on line 68

Warning: Cannot modify header information – headers already sent by (output started at …plugins/postman-smtp/Postman/PostmanUtils.php:68) in …public_html/wp-admin/post.php on line 197

Warning: Cannot modify header information – headers already sent by (output started at …plugins/postman-smtp/Postman/PostmanUtils.php:68) in …public_html/wp-includes/pluggable.php on line 1179

Here is my setting:
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