An invoice is a legal document, not just a bill
Most invoice templates found with a quick search look correct: a logo, a total, a due date. Fewer include everything actually required to be a valid, legally usable invoice, which matters the moment a client, an accountant, or a tax authority actually reads one closely.
What a valid invoice generally needs
A unique, sequential invoice number, since gaps in the sequence are one of the first things an audit checks for.
The full legal name and address of both the seller and the buyer, not just a trading name.
A clear issue date and, separately, the date the goods or service were delivered.
Each line item described specifically enough to know what was actually sold, not a single vague total.
The applicable tax rate and amount shown separately from the pre-tax price, not folded into one number.
Payment terms and due date stated explicitly, not assumed to be understood.
Where generic templates usually fall short
A downloaded template is built to look right, not to be correct in every jurisdiction. Tax rules, required fields, and even numbering rules differ by country, and a template built for one market can be missing a field another market requires by law.
The actual fix is not a better template
The fix is not memorizing a better checklist by hand, it is not building each invoice from a template at all. A generator that fills in the required fields, keeps the numbering sequential automatically, and applies the right tax treatment removes the chance of a missing field entirely.
Tootela's invoicing module was built around exactly this: sequential numbering, the required fields for the country it is issued in, and the same client and product data already in the CRM, so a correct invoice takes one click instead of a template and a hope.