You will have to use List validation settings for your requirements.
Use list validation formula like:
=IF(ISBLANK([Approval Date]),TRUE,IF(ISBLANK([Total Budget Amount Approved]),FALSE,TRUE))
OR:
=IF(ISBLANK([Approval Date]),TRUE,NOT(ISBLANK([Total Budget Amount Approved])))
Follow my answers given in below threads to add formula in List validation settings:
- List validation to make multiple fields mandatory if dropdown meets condition
- How to have validation for calculated column
Note:
- Sometimes comma(
,) does not work in formula (it is based on language or regional settings on your site). So in that case use semicolon(;) instead of comma(,).
- Use correct display name of your SharePoint columns in above formula.
- Wrap column names inside
[] if your column name has space in it. For example: [My Column Name].