API connection to Postmark stopped working after toggling Bot Fight mode On and Off

We had to enable the Bot Fight mode (Free tier) and raise our Security setting to Medium yesterday because we were under attack. Doing so appears to have broken our integration with the Postmark API for automated emails. We have since disabled the Bot Fight mode, and set our Security setting to Essentially Off, but the Postmark API still fails with the error:

Failed to connect to 18.216.28.119: Invalid argument
(The IP address varies)

I set the Postmark process to verbose debug but all I get is:

JSON: {“Subject”:“TheSubject”,“From”:""OurCompany" “,“To”:”"TheRecipient" “,“ReplyTo”:”"TheReplyTo" ",“TextBody”:“TheBody\n\n”,“Tag”:“TheTag”} Headers: Accept: application/json Content-Type: application/json X-Postmark-Server-Token: OurToken Return: Curl error: Failed to connect to 18.216.28.119: Invalid argument HTTP code: 0

This problem started exactly when we turned on the Bot Fight mode and set the Security to Medium. Nothing else has changed since. Our free Cloudflare setup is very simple. No rules other than a new WAF rule to Block the attacking AZN, and the problem appeared before I set that up.

Sort of feels like Cloudflare is still blocking the connection to https://api.postmarkapp.com/email even though the settings are back to what they were.

How can I troubleshoot this?
thanks!

Postmark confirms that they do not see our attempts at connecting. The connection is being blocked before it gets to them.

SOLVED. My host had blocked some IPs from Amazon Web Services in an attempt to help mitigate the attack when first reported yesterday. Turns out Postmark uses Amazon Web Services.

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