License question: freelancer vs clients

I am a freelancer who uses UNITY to make games for clients.

The clients have the apple accounts and android accounts in which they publish the game using their credentials. The clients also owns the source codes that we make making it their property.

Now, most of the time this clients does not want the unity splash screen, so I need to know if I, as the freelancer who will not make money from the game but got hired to build the game, should buy the unity pro license, or let the clients, who owns the source codes, buy the pro license for themselves.

It’s not allowed to mix and match personal edition with Pro. If you have personal edition and your client uses Pro to make the final build, then you are violating the license agreement. So, if you provide the client with a project, then you will also need Pro.