I suggest to adjust the datamodel then you have now a synthetic key between your billed and receipts table because they have more then one field in common (Date and Bill ID). This musn't be technically wrong but it's best practice to resolve such automatically generated synthetic keys/tables with own solutions to ensure that you understand your datamodel and also knows the quality of your data: Synthetic Keys
In your case this could be a composite key like:
Date & '|' & [Bill ID] as BilledReceiptsKey
But it could be that these composite key covered not each case (maybe some dates and/or bill id's are in one table and not within the other or reverse) and you need to transfer some fields from table to another (per joining or mapping) and/or fill up missing data/links and/or to create a link-table between them. Further I could imagine that these dates couldn't be simply associated because they are more a chain of events and you need to harmonize them per Canonical Date.
I think you will need to dive deeper in your data to determine which data are related to eachother in which way - indepent from their origin fieldnames which might give an orientation but not more.
Yes it meant that qlik has generated a composite key from all those fields. How to solve? Probably you need to do several things, for example to divide fields like Client Name, Client Group, Partner City into dimension-tables, creating of composite keys between them and/or creating of a link-table.
It won't be easy for as beginner but there is no way around then to learn these datamodel basics. For this I suggest like above mentioned to investigate your data carefully and to read the guidings within: Get started with developing qlik datamodels and the other links.
Further helpful to start is to going forward step by step - this meant to load at first one table and then examining it, then comes the next table which must be merged or associated and again it will be examinated within the gui per listboxes and charts and then follow the next table ... This ensured that you keep on overview and could learn and avoids an unsystematically trial and error approach with rather accidental results.