Sendgrid Copilot plugin send to list of emails with list of substitution tags

I am sending a dynamic template email in Sendgrid to multiple emails in one API call. This is important because it will need to go out to >10k people within an hour. Initially, I was doing this by scheduling a workflow on a list. But this will be slow/workflow intensive/costly for this volume.

I’m testing with @copilot 's excellent Sendgrid plugin. I’m passing a list of email addresses to the ‘To email address field’. The emails are all going out, so far so good.

The snag is, I’m trying to personalise the email for each recipient. My use case is there is a button in the email content with a link that is personalised for each user. I’m passing a list of links in the substitution tag. But when I open the emails sent by Sendgrid, the full list of comma separated links is sent to every recipient rather than just the personal link for that recipient.

Has anyone else come across this? I guess, a more common example would be sending to multiple recipients and passing each recipient’s first name in the substitution tag.

Help would be appreciated!