Array and string offset access syntax with curly braces is deprecated

[bartrylant]

When using any of the campaign monitor related plugins, I get

Array and string offset access syntax with curly braces is deprecated

Steps:
Install the craft-campaignmonitor-service plugin
Install the lists plugin
In the left sidebar, click on "Campaign Monitor Lists"

Or
Install the craft-campaignmonitor-service plugin
Install the transactional email plugin
Try to send a transactional email

PHP version | 7.4.6
Craft Pro 3.4.25

[heymarkreeves]

I'd been getting that, too, when updating my dev environment beyond PHP 7.3.9. I hadn't realized it came from my plugins. I was sticking to 7.3.9 and assumed it was a Craft thing.

I'll take a look at this. Thanks for pointing it out!

[heymarkreeves]

It looks like we're waiting for Campaign Monitor to update their libraries. See campaignmonitor/createsend-php#104.

I don't think I've every used {0} to get an array (or string) offset! The issue is outlined here.

[timbertens]

This has been updated a while ago, see campaignmonitor/createsend-php#101
As of version 6.1.1 of /campaignmonitor/createsend-php this should work fine