Unable to see fail error while submitting A SharePoint list form customized power apps

[AdminRishu]

Hi Everyone
I have a SharePoint Online list (Modern Experience) under that list I have some columns. Among all, there are 3 columns two are "date and time"  type column and one is "calculated" column.
So one column name is "start date" another column name is "end date" and 3rd column name is "total number of days" .
This list is for the leave request application, so if I will go on leave from 3rd June to 5th of June and if there is no weekend (Saturday-Sunday)in between that than the "total number of days" would be 3 which means I will start my leave on 3rd and my leave will end on 5th then I will be in office on 6th, so to achieve this I have kept some validation.
Column Validations are :
Start Date formula is =[Start Date]>=TODAY() (this means user will not be able to select any past date) 
End Date formula is =[End Date]>=TODAY()  (this means user will not be able to select any past date)
Total number of days =IF(OR(ISBLANK(Start Date ),ISBLANK([End Date ])),"",IF([End Date ]=Start Date ,1,[End Date ]-Start Date +1-(INT(([End Date ]-Start Date +1+MOD(WEEKDAY(Start Date )-1,7)+1)/7)*2)-IF(OR(WEEKDAY(Start Date )=7,WEEKDAY(Start Date )=1),1,0)-IF(OR(WEEKDAY([End Date ])=7,WEEKDAY([End Date ])=1),1,0))).  (this will count total number of days except Saturday and Sunday)

I have done a list validation also :=[End Date]>=Start Date. (this means and it will always be greater than start date)

As we know that I have put these many validations And all these fields are mandatory so whenever user is trying to submit the form without filling the value or without filling the appropriate value it is showing the error message over the former screen only (PFA).
Similarly when I have customized the same form into the power app it is not displaying the error message properly it is showing something related to patch functioning (PFA).

SharePoint List Error for not selecting mandatory fields in SPO List Default form:

SharePoint List Error for not selecting proper value in validated columns (List validation)

and now I have customized the same form in power apps and published the same it is saving the data in the same list but while occurring any error it is not displaying the proper error message, it is showing "Network error when using Patch function: The requested operation is invalid." and  "The requested operation is invalid. Server Response: Leave Rqst App For Flow failed: List data validation failed. clientRequestId: ba5b7163-3495-45f2-8058-28a665c6f480 serviceRequestId: ba5b7163-3495-45f2-8058-28a665c6f480".

PowerApps customized Form error  for not selecting and filling the proper values:

So I'm seeking help from any one of you to please tell me how to replace these errors messages And to display the exact error message which I am displaying on SharePoint form.
One more thing I want to understand that is it possible to remove OK button from date selection calendar page (PFA) . And another question is, if I will select 9 June as a start date so can we have an option to grey out the end date section for all the dates before 9 June. So user have to select the end date which is equal to or greater than 9 June.

[AdminRishu]

Hi All, @WarrenBelz , @Amik , @BCBuizer , @mmbr1606 
May I have a little help from anyone of you, I am very new to PowerApps Customization Form of SharePoint List. I just want to see all the validation errors on PowerApps Customized For because the same errors I can see on default SharePoint List form. If I will not be able to remove the errors then I have make it on List only 

    

[BCBuizer]

Hi  @AdminRishu ,

What you may do is to set a check in the OnChange property of the control which will display a notification if a certain condition is (not) met, for instance for a datepicker:

If(
    Self.SelectedDate < Today(),
    Notify("Please select a date from today onwards", NotificationType.Error)
)

Since this method will not capture events where the user does not give an entry, you will want to set up something in the OnSelect property of the submit button as well, for instance:

If(
    IsBlank(TextInput1.Text),
    Notify("You cant't leave field X blank", NotificationType.Error),
    IsBlank(DatePicker1.SelectedDate),
    Notify("You cant't leave field Y blank", NotificationType.Error),
    DatePicker1.SelectedDate < Today(),
    Notify("You cant't select a date in the past for field Y", NotificationType.Error),
)

In case you want to match the SPO OOB experience more and are willing to put in the work, this blog will guide you in the direction to do that: Data Validation For Power Apps Forms - Matthew Devaney

[AdminRishu]

Thanks a lot @BCBuizer for your help, I will try the same get back here. Meanwhile do you have any idea about removal of "ok" and "cancel" button from Data field. 

[BCBuizer]

Hi @AdminRishu ,

Those buttons cannot be removed from the classic date picker control. Using a modern data picker control, those are not present, but since that control is still in preview that is not recommended for use in production: