I see that this Slack is nearing its limit of free messages. I would strongly recommend considering a move to Zulip, for the following reasons:
• It's an Open Source replacement for Slack with a similar business model and philosophy to
cal.com. It can be self-hosted, or there's a SaaS hosted service in order to save time having to manage it yourself.
• Zulip Cloud Standard is free for open-source projects!
https://zulip.com/for/open-source/
• It's actually
significantly better than Slack:
https://zulip.com/why-zulip/
• There is a stupidly easy and seamless migration path from Slack which preserves all old messages:
https://zulip.com/help/import-from-slack