WP Printable Gift Certs Stopped Working

We’re getting the following error when trying to purchase a gift certificate:
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HTTP Status 405 – Request method ‘POST’ not supported

type Status report

message Request method ‘POST’ not supported

description The specified HTTP method is not allowed for the requested resource (Request method ‘POST’ not supported).

Apache Tomcat/5.5.15-150

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Can someone send me in the right direction to find out what’s wrong?

https://www.ads-software.com/extend/plugins/wp-gift-cert/