Displaying a message on clicking a button

I have created a button to generate a payslip of an employee.
How do I prompt a message to the user to say that the “Payslip successfully generated” after clicking the button?

You must use a wizard for that.
But it is not the common practice in Tryton. The form on which the button is clicked usually shows that it has changed (like the status or a check box etc.).

How to activate a boolean field on clicking the button?

The method of the button should write on this boolean.

You may use Bus Publish - Notification for Show Notification to user

Example Sending Notification

def mark_as_beneficiary(cls, records):
    for record in records:
        record.is_beneficiary = True
        if record.ifsc_code:
            regex = re.compile("^[A-Za-z]{4}[a-zA-Z0-9]{7}$")
            if (regex.match(record.ifsc_code)):
                record.ifsc_code = record.ifsc_code.upper()
                record.raise_user_error('Please fill valid IFSC code.')
        if record.account_no:
            if record.account_no.isnumeric() is False:
                    'Account No should be Numeric. Please fill valid Account No.')

The above code is not working as well as not showing any error on clicking the button mark_as_beneficiary. On clicking the button mark_as_beneficiary it should automatically make the boolean field is_beneficiary = True.
Any help regarding the issue will be grateful.

You must call ModelSQL.save on the records to get the changes persisted.