I created a campaign which send emails every 3 days however when look at the SendGrid report I can see only the first and second messages are being sent.
For example I look at campaign report, yesterday 200 emails are supposed be sent out but on sendgrid report only 100 requests were received. Anyone has an idea what could be the problem, please?
So for one it looks like there is a permission problem. I do not know exactly what this is but a precaution would be to change the owner of the entire mautic directory to www-data, this is done by running: chown -R www-data:www-data /var/www/mautic/*
Second it would be good to see your cronjob to make sure they are setup correctly.
Another thing that pops to mind is to make sure your SendGrid plan is correct, if it is only sending out 100 mails per day, this is generally the default package SendGrid gives to free accounts. But then again you say SendGrid only received 100 requests, so maybe not this.