What is the maximum length for a payment id field?

[dabedala]

Hi Team,

Need to know payment id field max-length, and specifications (any allowed special characters?)

Documentation only mentions it is a String:

id required

Unique identifier for the payment attempt. Used as the idempotency key. It can be assumed that requests with a given ID are identical to any previously received requests with the same ID. This ID must be surfaced to the merchant so that they can correlate Shopify orders with payments managed by the Partner app.

String

Thanks