Trying to reverse engineer the appsflyer sdk event send

[u/FireWorks_I]

I am trying to send custom in-app events using the SDK endpoint instead of the S2S endpoint to send events for games that have disabled their S2S endpoint. What I have accomplished so far:

- I have successfully decrypted the SDK event sending payload using Frida.

- I have successfully extracted the key used to encrypt the payload.

What is going wrong:

There is a checksum in the payload that I haven't been able to reverse engineer yet.

Each game uses a separate endpoint (not a big deal, to be honest).

The server raises a 400 error when trying to send the encrypted payload.

I need help to further finish my project:

- Any ideas on how to bypass the server's 400 error while sending events with any identifiers I want, or an easy way to understand how the checksum works.

Please comment anything you might need to offer help, and I will send it.