This code is meant to execute a F# Query against an EF DbContext, using quotations to isolate the repeating

let db() = serviceProvider.CreateScope().ServiceProvider.GetRequiredService<IMyDbContext>()
let usingDb f = db() |> f

let fff qq : IPounceDbContext -> IQueryable<_> = 
    let a = LeafExpressionConverter.QuotationToLambdaExpression(qq)
    let b = a.Compile()
    b

let ff qq = usingDb (fun db -> ((fff qq)(db)).SingleAsync())

member __.ReadRepo(userEmail: string, key: string) = 
    <@ fun (db: IMyDbContext) -> query {
        for userRepo in db.UserRepos do
        join user in db.Users on (userRepo.UserId = user.UserId)
        where (user.Email = userEmail && userRepo.Key = key)
        select userRepo.Value } @> |> ff

When calling

let a = LeafExpressionConverter.QuotationToLambdaExpression(qq)

at run time, the following exception is thrown

InvalidCastException: Unable to cast object of type
‘System.Linq.Expressions.MethodCallExpression1’ to type
‘System.Linq.Expressions.Expression1[Microsoft.FSharp.Core.FSharpFunc2[{OMITTED NAMESPACE}.IMyDbContext,System.Linq.IQueryable`1[System.String]]]’.”)

What is the problem?