How to handle firebase transactions offline? Swift

[bibscy]

I am writing an IOS App in Swift and I am using Firebase as a database. In this app multiple users can simultaneously read a list of jobs .
Depending on the boolean value of a job only one user should be allowed to write to that job (node) and change its’s boolean value.

1. After a write is completed at Users/UID/cus/bookingNumber , I need to save the same data to a different node, Cleaners/UID/bookingNumber.

First scenario would be to write to the first path in the body of the transaction runTransactionBlock and write to the second path in the completion handler, but Firebase Transactions (as per documentation) are not persisted across app restarts so there us a high risk that the database will be left in an inconsistent state.

2. Second scenario would be to attempt to write to both paths Users/UID/cus/bookingNumber and Cleaners/UID/bookingNumber in one single transaction (not using the completion handler) , but I haven’t found any tutorial/documentation on how to write to multiple paths using firebase transactions. I want to use Firebase transactions because I don’t want multiple users to claim the same job. Only one user should be allowed to claim a job at a time.

I asked a question on stackoverflow too.

Firebase: How to update multiple nodes transactionally? Swift 3

My data model

1. Claim - Cleaner
   cleaner tries to claim booking at Users/UID/cus/bookingNumber

   if FIRMutableData contains a key ‘claimed’ or key:value “claimed”:true 
   
     write at Users/UID/cus/bookingNumber with
       cleanerUID:UEWUW*932324jkjsdf
    	 timeStampBookingClaimed:435353
    		    claimed:true
   
   
   1.1 write to Cleaners/UID/bookingNumber
        original booking containing updated data