D8/9 - Fix contribution amount to be used as hidden field

[jitendrapurohit]

Overview

Allow contribution amount to be typed as a hidden field.

Before

In d7, the contribution amount field could be converted to a hidden field with a default value.

D9 - there is no way via UI, we need to modify the source and set it to type: hidden. But we still get a notice error on display.

After

Fixed. CiviCRM Number field can be changed to Hidden field via build form.