I was trying to find a way to post an arbitrary safe transaction (from my PC or server, does not matter) that would prompt a user to sign this transaction in the Gnosis Safe mobile app and browser extension.
Seems like I can only post transaction on-chain in GnosisSafe contract (using method execTransaction) if it is signed by two signers already, so it appears I need to use Gnosis API.
Also, seems like there are at least two Gnosis APIs:
1. Relay service (https://safe-relay.staging.gnosis.pm/api/v1/)
2. Notification service (https://safe-notification.staging.gnosisdev.com/api/v1/)
But I could not find any documentation except swagger, which does not explain much. Are these APIs open for public use and if there are any docs? In particular, how to use notifications API to send a signed message to request a transaction signature from mobile app and browser extension? Also how to format signatures for Relay API? Does it require decimal integer numbers?