Hi, I'm also having the same issue when formatting a DateTime parameter in a TextBox.
Here's what I have:
Estimates - from {Format("{0:dd/MM/yyyy}", Parameters.startDate.Value.Date)} to {Parameters.endDate.Value}and I get the following error:
ReportNameTextBox.Value expression [Estimates - from {Format("{0:dd/MM/yyyy}", Parameters.startDate.Value.Date)} to {Parameters.endDate.Value}] is not valid: Error evaluating embedded expressions: Unexpected token inside an expression at index 29