Step 1. Add two new fields named "Amount" and "Memo" to your data source. The "Amount" field will be of type double, the "Memo" field will contain text so it could be a string: NVARCHAR(MAX) or something like that depending on your database and data provider. Modify your select/insert/update queries to include those fields.
Step 2. Add custom field mappings for the non-standard (custom) appointment fields, which have "Amount" and "Memo" names in the data source. You can do it in VS Designer in the markup or using the property grid (ASPxScheduler control ->Storage->Appointments->CustomFieldMappings). You may decide to add mappings at runtime instead. In this case, use the following code in the code-behind file for the page containing ASPxScheduler control (Default.aspx.cs or Default.aspx.vb if you use Visual Basic), :