You may see in Framework logs or the Mosaic Error screens (21.2 customers above) the error:
'IllegalArgumentException: DateRange Start Date must be before or equal End Date'
Looking at the 'Caused By' area of that error stack, you see to add to that:
'carepackage.logic.budget'
This is dealing with the Budget area of the Mosaic finance functionality.
This error is typically caused in Mosaic for two known possible reasons where they data can become illogical:
Package budget details data that is effectively cancelled with start date after end date, and not in cancelled state.
Orphaned data left where a care package is cancelled on the care package screens when an open budget step had already begun creating data beforehand.
This may cause you to be unable interact with purchase step in ways such as resuming, saving, completing, amending, and removing services, and generating contributions.
You may see a clear error screen, but where there is a blank white screen, this kind of error will sit in the Framework logs.
This currently is remedied with a script fix to correct the data and tidy the cancelled elements across all the various tables. Please raise a new case online and reference the title of this article.