While it may be tempting to reuse the id field returned by the /actions endpoint, this is unsupported. The id field should not be considered stable, and the key field should instead be used.
To hardcode an action, first make a request to the /actions endpoint, filtered by App using the app query param (e.g. /actions?app=dc4dfc3e-c5bd-47a4-ac85-6d5ef8a50c50).
1

Store the App ID

This ID is guaranteed to remain the same for a particular App, even as different versions of the App are promoted in the background.
2

Look up the list of Actions by App ID

i.e. /api/v2/actions?app=768dedb4-54b8-4585-a166-2140216e9b13
3

Filter for the Action required using the `key` field.

This is the value provided in the Zapier Developer Platform, and remains the same for the same action across versions. The Action ID field returned can then be used to execute Actions or create Zaps.