WhatsApp's own help page for click to chat says the link is https://wa.me/ followed by the full phone number in international format, and that you should leave out zeros, brackets and dashes when writing the number. Its example of a wrong link includes a plus sign, so the plus goes too. That is the most common reason a link opens an error page.
In practice it means a UK number written 07123 456789 becomes 447123456789: drop the leading 0, add the country code 44, and remove spaces. A number written +91 98765 43210 becomes 919876543210. This tool applies the same steps, and tells you when the length does not fit the country you picked.
WhatsApp documents the pre-filled version as the same link with ?text= and the message after it, URL-encoded. A space becomes %20, a question mark %3F and so on. If you skip the encoding, parts of the message can be cut off or the link can break. The tool encodes it for you and shows a preview of the chat bubble.
The message only waits in your customer's text box. They still press send, so keep it short and let them finish the sentence. A line such as "Hi, I would like a quote for..." works better than a long script.
Put the link on your website button, Instagram bio, Google Business Profile, email signature and invoices. Print the QR code on a shop window, a menu, a delivery bag or a business card, so people can start a chat without typing your number. Download the PNG for print and the SVG when a designer needs a sharp vector.
Test the link on your own phone before you print anything. Click to chat only works when the person you link to has an active WhatsApp account. If you want replies at any hour, a link is the front door and a WhatsApp chatbot handles what comes next.
Typing the number with a leading + or 00, forgetting the country code, or keeping the 0 that is used for local dialling. Using a personal number on a printed QR code you cannot easily change. Writing a pre-filled message that sounds like an advert. And printing 5,000 flyers before checking that the link opens the right chat.
