stored proc formula returning null

it is returning yesterday's date.

is it possible that you mixed @startDate and @startingDate?

I think so because after the DECLARE,
I did
Begin
   Set @startdate=@startingdate
    Set @enddate=@startingdate
End

that maybe the problem

without knowing where are these lines, it is just impossible for me to say if it is the issue or not!

This variable is returning null  Declare @startDate date = Isnull(@startingdate, Dateadd(day, -1, cast(Getdate() as date)))

No, it isn't.  It's not possible for that expression to return NULL.  Something else must be happening to cause this problem.

Tested on my instance:
DECLARE @startingdate Date = NULL;
Declare @startDate date = Isnull(@startingdate, Dateadd(day, -1, cast(Getdate() as date)))
PRINT @startDate
2021-05-21

GetDate gave: 2021-05-22 13:14:34.717

Microsoft SQL Server 2017 (RTM-CU23) (KB5000685) - 14.0.3381.3 (X64)   Feb  9 2021 12:08:50   Copyright (C) 2017 Microsoft Corporation  Developer Edition (64-bit) on Windows 10 Home 10.0 <X64> (Build 19042: ) (Hypervisor)

The same on:
Microsoft SQL Server 2019 (RTM-GDR) (KB4583458) - 15.0.2080.9 (X64)   Nov  6 2020 16:50:01   Copyright (C) 2019 Microsoft Corporation  Developer Edition (64-bit) on Windows 10 Home 10.0 <X64> (Build 19042: ) (Hypervisor)

I think my mistake was I set the variables twice

thanks to all

[Withdrawn]