A handwritten receipt scribbled on a notepad generally counts as a valid record in most places, as long as it has the essential information — but "technically valid" and "actually holds up well" aren't quite the same thing.
What handwriting doesn't change, legally
In most jurisdictions, there's no requirement that a receipt be printed rather than handwritten — what matters is the information it contains (amount, date, what was purchased), not the medium it's written in.
Where handwritten receipts actually fall short
Legibility is the real practical problem — a handwritten receipt that's hard to read months later during a dispute or audit doesn't do its job even if it was technically filled out correctly at the time. Consistency is another: handwritten details vary receipt to receipt in ways a template doesn't.
Duplication and record-keeping
A printed receipt (especially digital) is trivially easy to keep a copy of for your own records. A handwritten receipt often exists as a single physical slip with no backup unless you separately photograph or log it.
Perception matters too, even if it's not strictly legal
A printed, itemized receipt signals a more established business than a handwritten note, which can matter for larger transactions or first-time customers forming an impression of your business.
When handwritten genuinely still makes sense
For very small, informal transactions, or in situations without power or a device on hand, a handwritten receipt with the core details is far better than none at all — it's a reasonable fallback, just not the default to build a business around.