Use the InvocableMethod annotation to identify methods that can be run as invocable actions. Invocable methods are called with the REST API and used to invoke a single Apex method.

Invocable methods have dynamic input and output values and support describe calls.

For more info, check the below link

https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_classes_annotation_InvocableMethod.htm

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