So I debug #Mailjet API myself and it's VERY funny,
First the error message :
"A template language occurred when sending a message using Template 2360961: stoi"
So first you need to dig in your template for finding weirdiness, but I'm used to other errors of Mailjet, that's not looking like a regular error message.
A regular error message look like this
Sometimes ago, I had a similar error but after looking at my sended payload, my code sended huge payload to Mailjet with too many Variables for the template, at this time, I fix the issue by just sending what I needed, and it fix the problem.
So I start to reproduce the issue.
But this the payload wasn't huge like the other time, only some variables like 30 of them.
So I start to narrow the problem with a simple technique : Dichotomy, You take the payload and you half it after each try.
"curl -s -X POST --user "$MJ_API_KEY:$MJ_API_PASS" https://api.mailjet.com/v3.1/send -H 'Content-Type: application/json' -d @firstname.lastname@example.org"
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