You have only up to 250 bytes (not characters) for your backend search terms on Amazon, which is roughly equivalent to 50–75 words depending on the length.
So, use spaces to separate words, and Amazon doesn’t recognize commas.
It is important to keep your backend keywords clean and relevant. so, avoid using common stop words like "a," "for," or "and," as they don’t add value for search indexing.
Additionally, don’t include brand names (unless you own the brand) or competitor ASINs. Focus solely on relevant long-tail phrases that didn’t fit naturally into your product title or description to ensure maximum visibility.