Determine whether your target is a function (read-only, uses GET) or an action (may have side effects, uses POST); and whether it is bound (scoped to a specific entity record) or unbound (org-level).
Call an unbound action via POST https://<org>.crm.dynamics.com/api/data/v9.2/<ActionName> with a JSON body supplying the action's parameters.
Call a bound action via POST https://<org>.crm.dynamics.com/api/data/v9.2/<entitySetName>(<recordId>)/Microsoft.Dynamics.CRM.<ActionName> with parameters in the body.
Call an unbound function via GET https://<org>.crm.dynamics.com/api/data/v9.2/<FunctionName>(Param1=@p1,Param2=@p2)?@p1='value1'&@p2=value2 using OData parameter aliases.
Call a bound function via GET https://<org>.crm.dynamics.com/api/data/v9.2/<entitySetName>(<recordId>)/Microsoft.Dynamics.CRM.<FunctionName>(Param=@p)?@p='value'.
Check the Dataverse Web API Action and Function Reference in the Microsoft Learn documentation for parameter names, types, and return type definitions for all built-in operations.
Known gotchas
Bound actions and functions require the full namespace prefix Microsoft.Dynamics.CRM.<Name> in the URL to distinguish them from entity set names; omitting the namespace causes a 404.
Function parameters must use OData parameter alias syntax (@p1, @p2) in the function call URL, with values supplied as separate query string parameters — inline literal values in the function path are not supported for all parameter types.
Custom API actions (registered via Custom API records) follow the same call pattern but use the publisher prefix in their name (e.g., cr123_<ActionName>) — always use the API's registered unique name, not its display name.
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