I am beginning to see the problem. Basically you have a lookup field and you want multiple selects in SharePoint and to use that field in PowerApps.
Frankly lookup fileds with multiple selections is always going to give problems in interfacing with other systems.
The way to work around is to have another "linkage" table (not sure what the technical term is) whereby it provides the multiple links between the two main tables.
Let me give you an example from my work. We have two tables; Transactions and Invoices. Any one transaction could be related to zero, one or multiple invoices (if for example you settle two or more invoices with one bank transaction).
There are two ways to link the invoices to the transactions:
- A lookup field in the Transactions table that gets its values from the Invoices table and has multiple selects
- Create a third table called TransactionsToInvoices that simply has two lookup fields as follows:
- One lookup to the Transactions table
- One lookup to the Invoices table
I am sure that by now you have guessed that 1. will not work with PowerApps (and a lot of other stuff) while 2. will be a little more fiddly at the start but will work with everything.
Please let me know if everything is clear so far or not, and if you need help to go further.
